Peter Killian Gallagher is an American actor. Since 1980, he has played roles in numerous Hollywood films. He is best known for starring as Sandy Cohen in the television drama series The O.C. from 2003 to 2007, and recurring roles in television such as Deputy Chief William Dodds on Law & Order: Special Victims Unit, Stacey Koons on the Showtime comedy-drama Californication, Nick on the Netflix series Grace & Frankie, and Director of Clandestine Services Arthur Campbell on Covert Affairs.
He also is known for his roles in the films Bob Roberts, The Player, Short Cuts, American Beauty, Mr. Deeds, and Palm Springs. In musical theatre, his most well known role is that of Sky Masterson in the 1992 Broadway revival of Guys and Dolls.