Kostja Ullmann (born 30 May 1984) is a German actor, best known for his leading role in the award-winning coming of age drama Sommersturm (Summer Storm) which gained a lot of praise throughout Europe.

He entered the stage at the age of eleven and performed at Hamburg's Ernst Deutsch Theater and Winterhuder Fährhaus.

In 2004, Kostja Ullmann made his movie debut in a leading role in Marco Kreuzpaintner's award-winning film Sommersturm (Summer Storm).

His performance in the romantic TV drama Heimliche Liebe (Secret Love) about the relationship of a schoolboy and an older woman won Ullmann the Günther-Strack-Fernsehpreis as Best Actor in 2006.

Directed by Angelina Maccarone, he plays a young delinquent who engages in an "amour fou" with his probation officer who is more than 30 years older than he is.