Simmons was born in Detroit, Michigan, to Patricia and Donald William Simmons. He has a brother and sister and attended the University of Montana.
J.K. Simmons has appeared in diverse projects spanning motion pictures, television and on and off Broadway. In film, he is best known as J. Jonah Jameson in Sam Raimi's Spider-Man trilogy and as Mac MacGuff in Juno; his other motion picture credits include Hidalgo, The Ladykillers, The Mexican, Off the Map, For Love of the Game, The Gift, Thank You for Smoking, Rendition, Burn After Reading, The Music Never Stopped, Jennifer's Body, Extract, The Vicious Kind, I Love You Man, Beginner's Guide to Endings, and the Academy Award-nominated film Up in the Air.
On the small screen, he is best known as Dr. Emil Skoda in multiple programs in NBC's Law & Order franchise, Assistant Police Chief Will Pope in TNT's The Closer, and neo-Nazi Vernon Schillinger in the HBO prison drama Oz. Simmons has also appeared on the Broadway stage in Guys and Dolls, Laughter on the 23rd Floor, A Change in the Heir, Peter Pan, and A Few Good Men.
In video games, he is best known for his work as Aperture Science's eccentric founder and CEO, Cave Johnson, in Valve Software's critically acclaimed physics game Portal 2.