Santiago Lionel Ascacíbar (born 25 February 1997) is an Argentine professional footballer who plays as a defensive midfielder for Estudiantes. He has also represented the Argentina national team. Ascacíbar began his career at hometown club Estudiantes. He then moved to Bundesliga team VfB Stuttgart in 2017, developing a reputation as a natural leader alongside criticism for his temperament. He completed a transfer to Hertha BSC in January 2020 after Stuttgart had suffered relegation the previous season, with manager Jürgen Klinsmann describing him as "one of the best defensive midfielders in the Bundesliga". Ascacíbar was part of the Argentine team that competed at the 2016 Summer Olympics. He made his senior debut in 2018.