Siyamthanda Kolisi (born 16 June 1991) is a South African professional rugby union player who currently captains the South Africa national team and also plays club rugby for the Sharks in Super Rugby and Western Province in the Currie Cup. He generally plays as a flanker. In 2018, Kolisi was appointed captain of the Springboks, becoming the first black man to hold the position, and eventually leading the South African Rugby team to victory in the 2019 Rugby World Cup Final against England. In December 2019, Kolisi was named in New African magazine's list of 100 Most Influential Africans.

Kolisi made his senior debut for Western Province against the Golden Lions during the 2011 Vodacom Cup and later in the year several injuries and international call-ups gave him the opportunity to make regular starts in the Currie Cup. He made 13 appearances and scored 4 tries during the campaign including a crucial score against bitter rivals the Blue Bulls.

2012 saw Kolisi graduate to the Stormers squad and he made an immediate impact with 16 appearances during the season and 1 try. The second half of the year was not so kind to him as a thumb injury restricted him to just one appearance in the 2012 Currie Cup and he had to watch on from the sidelines as Province lifted their 33rd Currie Cup title.

Kolisi was selected as the new captain of the Stormers on 20 February 2017. He was selected as the new captain of the Springboks on 28 May 2018, becoming the team's first black captain in its 126-year history. Bryan Habana, former Springbok and of mixed race, praised Kolisi's appointment: "It's a monumental moment for South African rugby, and a moment in South African history."

Kolisi was on the board of directors of MyPlayers Rugby which is the players' Organisation of all the professional rugby players in South Africa.

Kolisi married Rachel Kolisi in 2016 and as of 2018 they have two children together: son Nicholas Siyamthanda (2015) and daughter Keziah (2017). Since 2014 Siya's half-siblings, Liyema and Liphelo, children of Siya's mother who died in 2009, have been part of the Kolisi household, after five years in orphanages and foster care in Port Elizabeth. Rachel, one year older than Siya, is from Grahamstown and worked as a marketing executive before taking on duties as a full-time mother. Kolisi is an outspoken Christian.

Kolisi and his wife launched a The Kolisi Foundation in 2020. The foundation provides personal protective equipment to healthcare workers and delivers food parcels throughout South Africa, with special attention paid to the Zwide township where Kolisi grew up.