Thomas Vermaelen (Dutch pronunciation: [ˈtoːmɑs fərˈmaːlə(n)];[5] born 14 November 1985) is a Belgian former professional footballer who played as a defender.

Following Robin van Persie's transfer to Manchester United in August 2012, he was named club captain but found first team opportunities limited due to the success of Arsenal's new first-choice defensive partnership of Per Mertesacker and Laurent Koscielny.

[9][10] After Kolo Touré surrendered the number 5 jersey to him upon joining Manchester City,[11] Vermaelen, with William Gallas, formed Arsenal's central defence pairing.

He made his long-awaited return against Bolton Wanderers in the fourth round of the League Cup, where he captained the side to a 2–1 victory at the Emirates Stadium.

In the following game, he converted a Robin van Persie corner, heading home Arsenal's only goal in a 0–1 victory over Everton at Goodison Park.

Manager Arsène Wenger has called him a defensive rock and his partnership with Laurent Koscielny is strong, enabling Arsenal to build from the back.

Vermaelen's performances forced Arsène Wenger to drop him for the pivotal Champions League game against Bayern Munich at the Allianz Arena.

Arsenal won 0–2, although it was not enough to progress to the next round through aggregate, but they were the first team to prevent Bayern from scoring that season, thanks to an assured performance from the defence and reserve goalkeeper Łukasz Fabiański.

[30] Per Mertesacker and Laurent Koscielny continued to partner each other at centre-back for the following games, until the former's red card against West Brom at The Hawthorns on 6 April 2013 gave Vermaelen a chance to reestablish himself in the team.

On 17 May 2014, Vermaelen won his only trophy with Arsenal as an unused substitute in the team's 3–2 win over Hull City in the 2014 FA Cup Final.

In the second game of his second season on 29 August 2015, Vermaelen scored his first goal for Barcelona, finishing from a cross to win a home match against Málaga.

[35] Vermaelen was an 81st-minute substitute for Javier Mascherano on 20 December as Barcelona won the 2015 FIFA Club World Cup Final against River Plate in Japan.

[36] On 18 August 2016, Vermaelen made his debut for the Rome club in a UEFA Champions League qualification play-off against FC Porto and was sent off for two yellow card offences after only 41 minutes.

[38] On 26 November 2017, Vermaelen was selected to start in Barcelona's 1–1 draw with Valencia at the Mestalla Stadium, covering for the suspended Gerard Piqué.

He retained his place in central defence for seven of the next eight fixtures, before picking up an injury, including Barça's 3–0 win at the Santiago Bernabéu Stadium against rivals Real Madrid.

[40] On 1 January 2020, Vermaelen won his first trophy in Japan, starting in Vissel Kobe's 2–0 victory over Kashima Antlers in the final of the 2019 Emperor's Cup.

[43] On 21 January 2022, the Royal Belgian Football Association announced Vermaelen's retirement as a player, adding that he would be joining the Belgium national team as an assistant coach ahead of the 2022 FIFA World Cup.

On 8 October 2009, he was named Belgium captain[45] prior to the games against Turkey and Estonia in the 2010 World Cup qualifiers, but could not prevent the Belgians from finishing fourth in their group.