is a German football coach and former professional player who played as a centre back. He is the current manager of the Arsenal Academy.

Mertesacker began his senior career after being promoted from the youth ranks at Bundesliga club Hannover 96, making his senior league debut in November 2003. He was soon dubbed \"the Defence Pole\" (\"die Abwehrlatte\") by German tabloids, and gained a reputation for his exceptional disciplinary record, going 31 league games without being booked. After various standout performances at Hannover, as well as starring for the Germany national team at the 2006 FIFA World Cup at age 21, he transferred after 74 league matches for Hannover to fellow Bundesliga outfit Werder Bremen, for a fee of €5 million later that summer. His tenure at the club was characterized for his ability to read play and stifle the build-up play to opposition attacks, establishing himself as a defender with a quiet-but-effective game, and a core-component of the Bremen team that won the 2009 DFB-Pokal, and finished as runner-up in the 2009 UEFA Cup.

After being singled out for praise for his performances at the 2010 FIFA World Cup, and with his contract at Bremen dwindling, he transferred to Premier League club Arsenal a year later, for a fee of £8 million. At Arsenal, Mertesacker quickly established himself as the first-choice centre back for the club, becoming a mainstay despite sharing several defensive partners over his first two seasons. He eventually built up a solid relationship with fellow defender Laurent Koscielny, and the duo would star as Arsenal ended their nine-year trophy drought by winning the 2014 FA Cup. He would later captain and score for the side in their retention of the trophy a year later, before becoming the club's outright captain in 2016. He would again star in his third victory of the trophy in 2017. However, injuries derailed the latter stages of his career at Arsenal, and was used sparingly during his final two seasons, being forced to retire in 2018.

At national level, Mertesacker played for Germany at the under-20 and under-21 levels, prior to debuting for the senior side in 2004 against Iran. Upon his debut, Mertesacker established himself as Germany's first-choice centre back for ten years, participating in UEFA European Championship in 2008 and 2012, as well as the 2006, 2010 and 2014 FIFA World Cups, winning the latter. He would retire from international competition following this win.

Mertesacker has developed other ventures, including the \"Per Mertesacker Stiftung\", a charitable foundation that helps support amateur sportsmen, and the poor. He would transition into coaching following his retirement, taking charge of the Arsenal Academy.