He is an American actor and scriptwriter, best known for his role as Roman Bellic in the video game Grand Theft Auto IV. Zumwalt began his acting career in 2004, playing a small role in the short film 16w. From then until 2008, he took small roles in low-budget films, television series and video game roles to make a living.
In 2008, Zumwalt was hired by Rockstar Games as a voice actor in their video game Grand Theft Auto IV, playing the role of protagonist Niko Bellic's cousin Roman. Upon release, Zumwalt's character was critically well-received due to his distinctive accent and humorous dialogue. To this day, Grand Theft Auto IV is still his most notable role.
In 2014 Zumwalt co-wrote the script for the dramatic thriller Urge, alongside Aaron Kaufman. He also co-wrote the screenplay for the 2015 independent film Flock of Dudes, alongside Bob Castrone and Brian Levin.