Denis Colin Leary (born August 18, 1957) is an American actor, comedian, writer, and director. He is known for his often biting comedic style and his chain smoking. Leary is the star and co-creator of the television show Rescue Me now in its fifth season.

Leary was born in Worcester, Massachusetts, the son of Irish Catholic immigrants. His mother, Nora, was a maid, and his father, John Leary (deceased), was an auto mechanic. Since both of his parents are from Killarney, County Kerry, Ireland, Leary holds both Irish and American citizenship. He graduated from Saint Peter-Marian High School, in Worcester. Through marriage, Leary is a third cousin of talk show host Conan O'Brien and has jokingly said on Late Night with Conan O'Brien that, "All Irish people are related."

Leary is a graduate of Emerson College, in Boston, where he was classmates with fellow comic Mario Cantone, who remains his close friend. Comedian Steven Wright and actress Gina Gershon also attended Emerson at the same time as Leary. At the school, he and Jodi Haffner co-founded the Emerson Comedy Workshop, a troupe that continues on-campus as of at least 2009. After graduating with the Emerson Class of 1979, he took a job at the school teaching comedy writing classes and maintained the job for five years. Leary was honored with an honorary doctorate and spoke briefly at his alma mater's undergraduate commencement ceremony on May 16, 2005 and is credited as "Dr. Denis Leary" on the cover of his 2009 book, Why We Suck.