Ioan Gruffudd Welsh: ˈjɔan ˈɡrɪfɪð (born 6 October 1973) is a Welsh actor. He first came to public attention as Fifth Officer Harold Lowe in Titanic (1997), and then 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 2007 sequel, William Wilberforce in Amazing Grace (2006), and Tony Blair in W. (2008).

His other film credits include 102 Dalmatians (2000), Black Hawk Down (2001), The Gathering (2003), Fireflies in the Garden (2008), The Secret of Moonacre (2008), Sanctum, Horrible Bosses, Foster (all 2011), The Adventurer: The Curse of the Midas Box (2014), and San Andreas (2015).

On television, Gruffudd has starred in the CW series Ringer (2011–2012), the ABC drama Forever (2014–2015), the Lifetime series UnReal (2016), Sundance/ITV's Liar (2017–2020), and the Australian series Harrow (2018–present).