Ivan Simon Cary Elwes (born October 26, 1962) is an English actor. He is known for his leading roles in The Princess Bride (1987), Robin Hood: Men in Tights (1993), and the Saw series. Elwes's other performances in films include Glory (1989), Days of Thunder (1990), Hot Shots! (1991), Bram Stoker's Dracula (1992), Twister (1996), Kiss the Girls (1997), Liar Liar (1997), Ella Enchanted (2004), No Strings Attached (2011), BlackBerry, and Mission: Impossible – Dead Reckoning Part One (both 2023).

Elwes has also appeared on television series such as The X-Files, Seinfeld, From the Earth to the Moon, Psych, Life in Pieces, Stranger Things, The Marvelous Mrs. Maisel, and Knuckles.

He is the third son born to interior designer/shipping heiress Tessa Kennedy and the late portrait painter Dominick Elwes, and is the brother of producer/agent Cassian Elwes and artist Damian Elwes. He was born and raised in London and attended Harrow. After graduating from Harrow, he moved to the US and studied drama at Sarah Lawrence College. He left school after two years to begin his film career. Elwes is politically active for causes such as protecting the environment and helping Native American peoples. He is married to Lisa Marie Kurbikoff, a stills photographer.