Former Mainz goalkeeper Loris Karius is on his way back to the Bundesliga, having joined Union Berlin on a one-season loan deal from English Premier League champions Liverpool.

bundesliga.com has dug up five facts on the former Germany youth international as he returns to home soil. After all, there is much more to the 27-year-old stopper than an infamous UEFA Champions League night in Kiev…

1) Early experience of England

Karius is best known for his time with Liverpool, but he actually got a first taste of English football as a 16-year-old, joining the Manchester City academy in 2009. The up-and-coming goalkeeper was scouted while playing for the Germany U16s, later explaining to TransferMarkt that he felt like "half of the English Premier League" was interested in signing him at the time.

"I played for the U18s and the reserves and was training every day with the first team, with Joe Hart who was a great guy and helped me a lot back then," Karius admitted to Sky Sports. "He was a great role model. But then I made a decision that I wanted to play first-team football regularly, and it was quite difficult for a young player, especially as a goalkeeper, so I thought I'd have to take a little step back to a smaller club."

Karius (c.) helped Liverpool knock his boyhood club Manchester City out of the UEFA Champions League in 2017/18. - OLI SCARFF/AFP via Getty Images

Karius remained in Manchester for two years before returning to Germany with Mainz in 2011. Though he never made a senior appearance for the club, it remains a key period in his early development. It also gave him the opportunity to get to know future Bayern Munich defender Jerome Boateng, who spent the 2010/11 season at City.

"Loris gets on particularly well with Jerome Boateng," Harald Karius, Loris's father, told SPOX at the time. "Loris has been with City for a year and a half and was able to give him a few tips on what to do in Manchester. The contact between the two is very good."

2) Mainz magic

Before his time in Manchester, Karius played for local clubs FV Biberach, SG Mettenberg and SSV Ulm 1846, before stepping things up by joining the highly rated VfB Stuttgart youth academy in 2005. But it was at Mainz that he really made a name for himself – not unlike two of the coaches he would play under, Thomas Tuchel and Jürgen Klopp.

"I was a little impatient for the first year and a half, things weren't moving fast enough," Karius explained. "I came back from Man City, and maybe I thought I could gain a foothold in the Bundesliga as soon as possible. But at 18 I was still young, it was up and down. When I got the chance one day, I was able to take it."

That chance came in November 2013, when Mainz's first-choice goalkeeper Christian Wetklo was suspended and stand-in Heinz Müller was injured for a home meeting with Eintracht Frankfurt. Tuchel had already handed Karius his Bundesliga debut following another Wetklo dismissal on 1 December 2012 – a date he bears on his body in the form of a tattoo – but this time the current Paris Saint-Germain boss decided to give the 20-year-old a proper shot. Mainz beat Frankfurt 1-0, and Karius started the remaining 22 games of the season, keeping nine clean sheets as the 05ers achieved an impressive seventh-place finish.

Karius (r.) garnered a reputation as one of Germany's best goalkeepers during his successful stint with Mainz, keeping 30 clean sheets in 91 Bundesliga appearances. - Alex Grimm/Bundesliga/DFL via Getty Images

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Tuchel left at the end of that season, but Karius remained Mainz's No.1 for the following two campaigns, under Kasper Hjulmand and Martin Schmidt. He only missed a solitary Bundesliga game during that period, emerging as one of Germany's best young keepers by keeping another 20 clean sheets and helping Mainz climb as high as sixth in 2015/16.

"If I analyse the three seasons at Mainz now, it was a great time all around," Karius said in June 2020. "In retrospect, it was the best decision to go to Mainz and take my first professional steps there."

3) Highs and lows in Liverpool

Karius joined Liverpool in summer 2016 after being snapped up by Klopp, who had previously spent seven memorable seasons as Mainz coach (2001-2008). Although he inherited the No.1 jersey at Anfield, the German keeper soon found himself competing with Belgium's Simon Mignolet for a starting berth. After recovering from a hand injury in pre-season, Karius started 10 games in the autumn of 2016/17, but was dropped to the bench following an error against Bournemouth.

"These players are all my boys – sometimes you have to push them and sometimes you have to protect them," Klopp told BBC Sport. "I know how strong Loris Karius is, but obviously he couldn't show it in the last one or two games. It's not a problem for me. It happens, that's life. But judging him in this moment makes absolutely no sense, because we have a long-term project, even with our goalkeepers."

Karius (l.) was brought to Anfield by fellow German Jürgen Klopp (r.), who also made a name for himself at Mainz. - Alan Martin/imago/Action Plus

Karius was forced to be patient for the rest of 2016/17, only appearing in the domestic cup competitions, but 2017/18 was a different story. Though Mignolet began the Premier League season between the sticks, Karius impressed in the group stages of the Champions League, keeping clean sheets in big wins over Maribor and Spartak Moscow. Klopp eventually restored him to his Premier League starting XI in January, as the young German produced noteworthy performances against Southampton and Newcastle and saved a late penalty from Tottenham's Harry Kane. In total, he kept 10 clean sheets in 19 top-flight appearances that term.

With Man City romping to the Premier League title, Liverpool's focus switched to the knockout stages of the Champions League, and Karius kept one of his six clean sheets in the competition as the Reds stunned Pep Guardiola's side 3-0 in the quarter-final first leg at Anfield. Klopp's side also resisted a fightback to beat Roma 7-6 on aggregate in the semi-finals, setting up what would be a fateful showdown with Real Madrid in the showpiece.

4) KO in Kiev

The 2018 Champions League final has become the defining match of Karius's career to date, with two high-profile mistakes allowing Karim Benzema and Gareth Bale to score as Real ran out 3-1 winners. A point that is rarely touched upon, though, is that the Liverpool keeper appeared to take a blow to the head in an earlier collision with Sergio Ramos. A subsequent evaluation by the Massachusetts General Hospital revealed he had sustained a concussion.

"He was influenced by that knock, that is 100 per cent," Klopp later stated, while revealing that Franz Beckenbauer was the one who suggested to him that Karius might have been suffering from concussion. "If you ask Loris, he says he didn't think about it and didn't use it for a second as an excuse. We don't use it as an excuse, we use it as an explanation."

A disconsolate Karius was left to rue what might have been after his errors against Real Madrid in the 2018 UEFA Champions League final. - Michael Regan/Getty Images

To what extent the concussion impacted Karius's performance is impossible to gauge, and may not have affected the outcome of the game at all – but there is no denying that he has struggled to shake off the stigma attached to his errors that night.

"Nobody cares when other keepers make another mistake, but it's always a big deal if I do," he recently admitted. "It's pretty extreme how differently things are interpreted. People have derived pleasure from it since the Champions League final. Some people don't understand or don't want to acknowledge that it was because of a head injury, and they criticise my performance or make fun of it. I just don't get it."

5) Bouncing back

The cruel nature of the Champions League loss and the arrival of Alisson Becker essentially spelled the end of Karius's time at Anfield, although he was still given a rousing reception by Liverpool fans when replacing the Brazil No.1 in a pre-season friendly with Torino. Shortly before the start of the 2018/19 season, it was announced that the German would join Turkish club Besiktas on a two-year loan deal.

"It's good for him," Klopp said. "I really think Loris is a fantastic goalkeeper, at a very good goalkeeper age. A lot of people have spoken to me about our improved defence. And as good as Alisson was in the last three games, in most of the games when we were already really good he was not here, it was still Loris in the goal. He did a lot of good things."

Karius's time in Istanbul was a mixed bag, with plenty of solid performances but also a tendency for observers to highlight his mistakes, such as when he was caught out by a deflected cross-cum-shot in a UEFA Europa League clash with Malmo. After 67 appearances over two seasons, including 14 clean sheets, he terminated his contract with the Süper Lig club in May 2020, before his return to Germany with Union was announced in late September.

"The club has to appeal to me, first and foremost," the 27-year-old said when asked about his next move earlier this year. "Basically, Germany appeals to me. It's my home country and I haven't been there for a long time."

Now Karius has his wish – after a four-year absence, he's heading back to the Bundesliga. In a curious quirk of fate, his first outing for his new side could come against the club where he got his first big break: Union host Mainz in the opening game of Matchday 3. It hasn't been an easy road for the boy from Biberach over the past few years, but he will be determined to continue on the path to redemption at the Stadion An der Alten Försterei.

"I'm looking forward to my new opportunity in Berlin and I'm happy to be playing in the Bundesliga again," Karius concluded. "Union is a special club, one that has earned a great deal of respect, not just by promotion to the Bundesliga. I would like to play my part in this positive development and help to achieve the great goal of staying in the Bundesliga."

About the clubs

1. FSV Mainz 05

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1. FC Union Berlin

An der Alten Försterei