Bayern Munich and Bayer Leverkusen have regularly found themselves at odds competing against each other for silverware - as they will do once again on Sunday in a top-of-the-table clash - but there are plenty of players with split allegiances come the Matchday 8 encounter.
At Leverkusen: 191 Bundesliga games (2001-2007)
At Bayern: 63 Bundesliga games (2008-2012)
Butt had a pretty extraordinary career and is perhaps best remembered as a goalkeeper who scored goals rather than prevented them. The 26 he netted in the Bundesliga is the most by a goalkeeper - all from the penalty spot. He missed only four league games between August 1997 and February 2007 with Hamburg and (from 2001) with Leverkusen, where he was first choice in the Werkself side that famously finished runners-up in the Bundesliga, DFB Cup and UEFA Champions League in 2002. The four-time Germany international scored eight times in 263 competitive appearances for Leverkusen, before leaving for Benfica in 2007 after being ousted by Rene Adler.
Watch: Penalty-taker Butt vs. instant karma
He was back in the Bundesliga a year later, though, when Bayern picked him up on a free. He made a total of 91 appearances over four years in Munich, sometimes being No.1 but sometimes back up. He became the first goalkeeper to score in regular time for the club when he converted a penalty against Juventus in the 2009/10 Champions League group stage - all three of his European goals actually came against the Italians, with one each for HSV, Leverkusen and Bayern. After the 2002 final, he reached the Champions League showpiece two more times with Bayern, in 2010 and 2012, but had already been demoted to No.2 behind Manuel Neuer by the time the latter came around. It was the second time he'd been a treble runner-up - the only Bundesliga player to suffer the fate twice. Butt retired at the end of that season.
At Leverkusen: 87 Bundesliga games (1989-1992)
At Bayern: 67 Bundesliga games (1992-1995)
Jorginho - full name Jorge de Amorim Campos - was at the dawn of the era of Brazilians donning the colours of Leverkusen, being the second of now 23 players from his nation to represent the Werkself. Already a silver medallist from the 1988 Olympics, he arrived on German soil a year later and would become the first Bundesliga-based player to play for Brazil and went to the 1990 FIFA World Cup. The right-back played 101 times for Leverkusen over three seasons, very often in an attacking wing-back role.
His displays caught the eye of those in Munich, and Bayern signed the Rio de Janeiro native in 1992. He immediately found his place in the team and started all but one Bundesliga game in his maiden campaign. Despite being less of a regular in the following season, he still picked up his sole Meisterschale before heading to the USA and playing every game as Brazil lifted the 1994 World Cup. He left Bayern in 1995 after 80 appearances - and 181 all told in Germany - as he moved to Japan before a return home for the final years of his career.
At Leverkusen: 127 Bundesliga games (1996-2001)
At Bayern: 94 Bundesliga games (2001-2005)
Robert's older brother Niko also played for both clubs and would go on to win the double as head coach at Bayern, but the younger Kovac spent more time with both teams and also made a direct transfer between the two in 2001. After starting at Hertha Zehlendorf in his native Berlin and joining from relegated Nuremberg, the defender's five-year stay at the BayArena saw him make 162 appearances and establish himself with the Croatia national team, going on to earn 84 senior caps.
He was then signed by Bundesliga and European champions Bayern in 2001 - re-uniting with Niko after he'd left Leverkusen for HSV in 1999 - and would spend four years as a mainstay of their defence, winning two domestic doubles in 2003 and 2005. He left with 144 appearances and a healthy trophy haul to join Juventus after the latter season. He then returned to the Bundesliga in 2007 with Borussia Dortmund.
At Leverkusen: 92 Bundesliga games (2001-2004)
At Bayern: 144 Bundesliga games (2004-2009)
Lucio started his playing career as a forward, and it showed when he made his transatlantic switch from Internacional to join a strong Brazilian contingent at the BayArena in January 2001. He would become a cornerstone of the side, making 122 appearances and notably scoring in the Champions League final defeat to Real Madrid in the notorious 2001/02 season, forming a dependable centre-back duo with fellow Brazilian Juan. Despite that setback, he went on to play every minute for Brazil as they won the World Cup that summer in Japan and South Korea.
Watch: Lucio's thumping free-kick for Leverkusen
And he was another who ended up making a direct switch from North Rhine-Westphalia to Bavaria, joining Bayern in summer 2004 on a six-year deal. "Lucio will be a big character in our new-look team," club chairman Karl-Heinz Rummenigge said, and was proved right as the no-nonsense Brasilia-born defender stacked up the silverware over five seasons that saw him play 218 games. Playing alongside the likes of Kovac, Valerien Ismael, Daniel Van Buyten and Martin Demichelis, Lucio won three domestic doubles and frequently stood in as team captain when Oliver Kahn was missing. His ability to start attacks by striding out of defence wowed Bayern fans as much as his capacity for snuffing out opposition strikers. "Naturally, we're sad he's leaving the club," then Bayern general manager Uli Hoeneß stated when Lucio joined Inter Milan in 2009.
At Leverkusen: 113 Bundesliga games (1998-2002)
At Bayern: 169 Bundesliga games (2002-2006, 2007-2009)
Ze Roberto had already had a short spell at Real Madrid and gone back to Brazil before trying to establish himself again in Europe by signing for Leverkusen in 1998. He did exactly that. One of the reasons he left Madrid was his lack of first-team opportunities, something that was never in question with Die Werkself where he missed just two Bundesliga games in his maiden season in Germany. Alongside compatriot Emerson and club legend Jens Nowotny, he helped turn the club's midfield into one of the most formidable and complete in European football. Leverkusen finished Bundesliga runners-up in three of his four seasons at the club, and his influence was such that it was no surprise he was eventually snapped up by Bayern after that infamous 2001/02 campaign.
Watch: Ze Roberto's best 5 Bundesliga goals
Four domestic doubles from 248 appearances followed for the Brazilian, the last coming in the 2007/08 season. That was his first since returning to Bayern on a two-year loan from Uruguayan side Nacional, having first left Munich upon the expiration of his contract. When he left Bayern a second time in 2009 to join Hamburg, the northerners could not believe their luck. "He's a technically excellent player and brings unbelievable experience with him," said then HSV boss Bruno Labbadia of the Brazilian capable of playing anywhere down the left or even central midfield.
At Bayern: 4 Bundesliga games (2009-2013)
At Leverkusen: 29 Bundesliga games (2013-2014)
Can was born in Frankfurt and spent time in the Eintracht academy before joining Bayern at U17 level in 2009. He moved through the ranks and featured twice in first-team matchday squads in 2011/12, before making seven senior appearances for the club the following season under Jupp Heynckes. Even then he was used as a utility player across midfield and defence. His sole Bundesliga goal for the Bavarians was when he got a touch off a Xherdan Shaqiri free-kick against Freiburg at the back end of the season.
The future Germany international was then snapped up by Leverkusen on a four-year deal. He quickly established himself as a first-team regular at the BayArena and played 39 times in all competitions, scoring four goals and again filling in at left-back, centre-back, central midfield and more as Die Werkself finished fourth in the Bundesliga. After one year in Leverkusen, he joined Liverpool before signing for Juventus and, most recently, Dortmund.
At Leverkusen: 117 Bundesliga games (2007-2011)
At Bayern: 79 Bundesliga games (2015-2018)
As you'll note, Vidal was the latest in a long line of South American players to take the first step into Europe with Leverkusen and later also star for Bayern. The Chilean arrived in summer 2007 from Colo-Colo - reportedly after director of football Rudi Völler personally made the trip to Santiago to convince him. He would go on to catch further eyes over four successful years at the BayArena, culminating with a runner-up finish in the 2010/11 Bundesliga behind Dortmund.
Watch: Every Vidal goal and assist for Bayern in 2017/18
After that, he joined Juventus and won four straight league titles in Italy before a return to Germany with Bayern in 2015, where he lifted the Bundesliga Meisterschale three times in as many years. The combative midfield all-rounder was a regular during his time at the Allianz Arena and made well over 100 appearances for Bayern before his 2018 departure for Barcelona. He's now back in Italy with Inter Milan.
At Leverkusen: 7 Bundesliga games (1999-2005)
At Bayern: 6 Bundesliga games (January 2009-March 2009)
The USMNT's record goalscorer in fact began his professional career in Germany with Leverkusen. He came through the Cal South Olympic Development Program that had also produced Saarbrücken and Bochum striker Eric Wynalda, but he was spotted by Werkself academy director Michael Reschke at a youth tournament in Europe and signed as a 16-year-old in 1999. The centre-forward was part of the Bayer youth side that won the U19 Bundesliga in 2000, coming off the bench in the final against Werder Bremen. He returned to the USA on a three-year loan with the San Jose Earthquakes, where he made a name for himself and won the MLS twice. Donovan made a total of nine competitive appearances for the Leverkusen first team in the second half of 2004/05, before returning to his native California permanently with Los Angeles Galaxy.
We'd see the 157-time USMNT international back in Germany in 2009. He spent three months on loan at Bayern during the MLS off-season. He was reportedly a target player for Jürgen Klinsmann, who was coach at the time in Munich. Donovan only made seven substitute appearances, but became the first American-born player to represent Bayern, with only Julian Green and Chris Richards to follow so far.
At Leverkusen: 114 Bundesliga games (1999-2002, 2010-2012)
At Bayern: 107 Bundesliga games (2002-2006)
One of the top midfielders in the world in the first decade of the millennium, Ballack was born in former East Germany. After cutting his teeth in the Bundesliga at Kaiserslautern, he truly made his name in the colours of Leverkusen. Given the freedom of Die Werkself's midfield by Christoph Daum and his successor as coach, Klaus Toppmöller, the all-action qualities that had seen him stand out at lower levels came to the fore in the German top flight. That was notably true in the 2001/02 season when he netted 17 goals in 29 Bundesliga matches to finish level with Giovane Elber and one shy of league top scorers Martin Max and Marcio Amoroso, both out-and-out strikers.
That season he collected a quartet of runners-up medals for club and country, but he did secure a transfer to Bayern where he would considerably swell his silverware collection. Ballack added three domestic doubles, and twice finished as Germany's Player of the Year - an award he had first won in his final season in Leverkusen - as he scored freely from midfield. After a successful four-year stint at Chelsea, he returned to Leverkusen in 2010. "I'm coming full circle with my transfer to Bayer Leverkusen," said Ballack, then the Germany captain. "I had a great and successful time here, which I look back on fondly. That comforted me in my decision." He retired in 2012 having made 155 competitive appearances for Leverkusen and 157 for Bayern, as well as earning 98 international caps.
At Bayern: 130 Bundesliga games (2006-2014)
At Leverkusen: 43 Bundesliga games (2009-2010)
Unquestionably one of the finest midfielders Germany has ever produced, Kroos joined the Bayern academy at 16 from Hansa Rostock in 2006, and was already training with the senior side by the second half of the season. Ottmar Hitzfeld promoted him full-time in 2007/08 and Kroos became the youngest person ever to play for Bayern's first team up to that point. After finding playing time limited under Klinsmann, the midfielder joined Leverkusen on an 18-month loan midway through 2008/09.
Watch: Toni Kroos, made in the Bundesliga
It was in the second season that he really established himself under Jupp Heynckes, even being named Man of the Matchday for three straight games by kicker as Die Werkself went on to finish fourth. Returning to Munich in 2010/11, he was the attacking midfielder under Louis van Gaal before finding himself under the tutelage of Heynckes again and reaching two consecutive UEFA Champions League finals as a key member of the 2013 treble-winning squad. After one more year at Bayern and a domestic double with Pep Guardiola, one of the world's finest passers joined Real Madrid in 2014.
At Leverkusen: 121 Bundesliga games (1993-1997)
At Bayern: 77 Bundesliga games (1999-2002)
Signed from legendary Brazilian club Corinthians in 1993, Paulo Sergio hit the ground running - and scoring - in Germany with Leverkusen. He struck 17 times in 32 top-flight outings in his maiden season to finish just one goal shy of the league's top scorers. He would match that tally in 33 matches in his final campaign with Die Werkself having endured a tougher time in between, but also winning the 1994 World Cup alongside club teammate Jorginho. He then moved to Roma where he teamed up effectively with the Eternal City's homegrown hero Francesco Totti.
Watch: Bundesliga Legend Paulo Sergio in Brazil
His two-year stay in the Italian capital was ended by his 1999 transfer to Bayern, who wanted to pair the Brazilian with compatriot Elber in the hope of wiping away the memory of the painful Champions League final defeat they had just suffered to Manchester United. Hitzfeld's side did so by winning the 2000/01 final in a penalty shoot-out against Valencia. After three years in Munich, the Sao Paulo native - a regular in Bayern's Legends team now - left for the UAE. He did so with two Bundesliga titles and a DFB Cup to go along with his Champions League medal in his bags.
At Leverkusen: 68 Bundesliga games (2009-2011)
At Bayern: 247 Bundesliga games (1987-1991, 2009, 2011-2013, 2017-2018)
Leverkusen were one of nine clubs Heynckes coached in his long career. He started at the age of 34 at Borussia Mönchengladbach - where he had spent most of his playing days. By the time he took over at Leverkusen in June 2009, he had already had one lengthy stint with Bayern as well as spells with Eintracht Frankfurt and Schalke. He had international experience too, serving as head coach of Athletic Bilbao (twice), Benfica and Tenerife, while he also won the Champions League with Real Madrid in 1997/98.
The former West Germany striker's two seasons with Leverkusen proved a great success. He brought in players like Finnish centre-back Sami Hyypia and midfielder Lars Bender, and also nurtured the development of players like Kroos, Vidal, goalkeeper Adler, Brazilian midfielder Renato Augusto and striker Stefan Kießling.
Watch: Bayern won the treble under Heynckes in 2012/13
In his first season Die Werkself started with a record 24-game unbeaten run before finishing fourth. In 2010/11 - with Ballack back at the club - they pushed Jürgen Klopp and Borussia Dortmund for the title as Leverkusen were Bundesliga runners-up for only the fifth time.
Heynckes was then tempted back to Bayern, the oldest head coach in the Bundesliga when he returned at the age of 66 in July 2011. It was already his third spell on the bench in Munich, having first been appointed in 1987 before winning back-to-back Bundesliga titles between 1988 and 1990 as well as reaching the European Cup semi-finals three seasons a in row. Former Bayern president Uli Hoeneß often said his decision to dismiss Heynckes in October 1991 after a rocky patch was the "biggest mistake" of his career, and he had called on him to serve as caretaker for a five-game period at the end of 2008/09.
The 2011/12 season was almost a roaring success for Heynckes, but Bayern ended it as runners-up to Dortmund in both the Bundesliga and DFB Cup as well as Chelsea in the Champions League. The heartbreak from that year drove Bayern on though, and in 2012/13 Heynckes' brilliant side captained by Philipp Lahm became the first German team to win a league, cup, and Champions League treble.