Ioan Gruffudd (Welsh: [ˈjɔan ˈɡrɪfɪð]; /ˈjoʊɑːn ˈɡrɪfɪθ/; born 6 October 1973) is a Welsh-American actor. He is known for his roles in film and television series in the United Kingdom, the United States, and Australia.

He was first noted for his portrayal of Harold Lowe in Titanic (1997) and for his portrayal of Horatio Hornblower in the Hornblower series of television films (1998–2003). Subsequent roles have included Lancelot in King Arthur (2004), Reed Richards/Mister Fantastic in Fantastic Four (2005) and its sequel Fantastic Four: Rise of the Silver Surfer (2007), William Wilberforce in Amazing Grace (2006), Tony Blair in W. (2008), and Adam Lockwood in Bad Boys: Ride or Die (2024).