Mark Alan Ruffalo (; born November 22, 1967) is an American actor, filmmaker, and activist. He made his screen debut in an episode of CBS Summer Playhouse (1989), followed by minor film roles. He was part of the original cast of This Is Our Youth (1996), for which he was nominated for an Independent Spirit Award. Following were his roles in 13 Going on 30 (2004), Eternal Sunshine of the Spotless Mind (2004), Zodiac (2007), and What Doesn't Kill You (2008). In 2010, he starred in the psychological thriller Shutter Island and the comedy-drama The Kids Are All Right. For the latter, he received nominations for the SAG Award, BAFTA Award, and an Academy Award for Best Supporting Actor. He also co-starred in the mystery films Now You See Me and Now You See Me 2 as FBI Special Agent Dylan Rhodes.

Ruffalo gained international prominence by portraying the Marvel Comics character Bruce Banner / Hulk in the Marvel Cinematic Universe (replacing Edward Norton, who headlined The Incredible Hulk, released in 2008), beginning with The Avengers (2012) and later reprising the role in Iron Man 3 (2013), Avengers: Age of Ultron (2015), Thor: Ragnarok (2017), Avengers: Infinity War (2018) and its untitled sequel (2019).

He starred in and was the co-executive producer of the 2014 television drama film The Normal Heart, for which he was nominated for the Primetime Emmy Award for Outstanding Television Movie and he won the Screen Actors Guild Award for Best Actor in a TV Movie. The same year, he portrayed Dave Schultz in Foxcatcher, for which he was nominated for awards, including a Golden Globe, and an Academy Award for Best Supporting Actor. In 2015, he was nominated for the Golden Globe Award for Best Actor – Motion Picture Musical or Comedy for Infinitely Polar Bear and also received BAFTA and Academy Award nominations for his role in the drama Spotlight.