The FIFA World Cup winner in 2014 had originally arrived at Dortmund from Bayern in 2008, but has since come full circle, and played a key role as the Bavarians eased to the Bundesliga title in 2017. Allow bundesliga.com to present some lesser-known facts about Hummels...
1) Football in the blood
Born in the western town of Bergisch Gladbach, Hummels was just six when his family moved to Munich after his father Hermann, a former Bundesliga 2 player with Schloß Neuhaus, took up the position of youth coach at Bayern, with Hummels Junior joining the German record champions' youth side.
2) Converted to centre-back
Mats was 14 when he came under Hermann's tutelage, but the future Germany star was granted no favouritism, instead spending his first few months in the side on the substitutes' bench. When he did play, he was employed as either a centre-back or holding midfielder, despite starting his career as an aspiring striker.
Watch: check out Hummels' remarkable tackle against Frankfurt on MD24 in 2016/17
3) Priorities straight
For Hummels, football has always come first. "We didn't use to go on holidays because Mats wouldn't want to miss a single game or training session," his mother Ulla Holthoff told 11Freunde. "Once we went skiing for a week, but he had a football tournament the day we left, so he just stayed home and joined us a day later by train. He was twelve at the time."
4) Dortmund open the door
Despite catching the attention of legendary Bayern coach Herrmann Gerland and, head coach at the time, Felix Magath, Hummels failed to break into the German record titleholders' first team during his time in Bavaria. Instead of languishing in the reserves, the centre-back was shipped out on loan to Dortmund during the January transfer window in the 2007/08 campaign. He went on to establish himself as one of the first names on the team-sheet, making over 200 appearances in all competitions, winning two Bundesliga titles and a DFB Cup before being named as the club's captain at the start of the 2014/15 campaign.
Watch: check out Hummels' top five goals in BVB colours
5) Surprise package
Hummels was a surprise regular in Germany head coach Joachim Löw's line-up for UEFA EURO 2012 and built a solid defensive partnership with Bayern's Holger Badstuber who, interestingly enough, Hummels had played alongside in defensive midfield at youth level when his father was still in charge at Bayern.
6) Praise from Zizou
He might be compared to Germany legend Franz Beckenbauer due to his ball-playing ability, but for Hummels, French playmaker Zinedine Zidane was No1. Being labelled "the most positive surprise" of EURO 2012 by the 1998 FIFA World Cup winner must have gone down very well indeed in the Hummels household.
7) All-star performance in Brazil
At the 2014 FIFA World Cup in Brazil, the man who once joined Lukas Podolski on the cover of FIFA '12 featured in all six games and scored twice, including the all-important winner in a 1-0 victory against France in the quarter-finals, as Germany went on to lift the trophy for a fourth time. The defender was not only named in the All-Star XI for the tournament, but he also made it into the Dream XI as voted for by users on fifa.com. "This is one of the best generations we've had in Germany," said Hummels after the 1-0 win over Argentina in the final.
8) Partner in crime
In a survey conducted by Sky Germany and the readers of Closer magazine, Hummels' wife Cathy Fischer was voted "Germany's most popular WAG 2013", and she's won another curious title: "Miss FC Bayern 2007". Fischer, who calls Victoria Beckham her idol, has been in a relationship with Mats since he was 18, and the two were married in June 2015.
9) Other side of the camera
His mother Holthoff is a well-known sports journalist and became the first woman to commentate on a football game on German television. Mats often went along to broadcasts when he was still a child and even considered working as a journalist himself. "The media is his home," explained Holthoff. "Whenever he has a match, there's at least one journalist saying, 'I remember when you were little.'"
Watch: Mats Hummels chats to Patrick Owomoyela in his final days as a BVB player
10) Avid reader
"Mats is a bookworm," says Ulla "He read a lot - even at a young age," which might well explain the defender's smooth-tongued interview technique. "He used to read comics in particular. He got his word play from Lucky Luke and Asterix."