The Academy Award for Best Actor is an award presented annually by the Academy of Motion Picture Arts and Sciences (AMPAS). It has been awarded since the 1st Academy Awards to an actor who has delivered an outstanding performance in a leading role in a film released that year. The award is traditionally presented by the previous year's Best Actress winner.

Cillian Murphy is an Irish actor. He made his professional debut in Enda Walsh's 1996 play Disco Pigs, a role he later reprised in the 2001 screen adaptation. His early film credits include the horror film 28 Days Later (2002), the dark comedy Intermission (2003), the thriller Red Eye (2005), the Irish war drama The Wind That Shakes the Barley (2006), and the science fiction thriller Sunshine (2007). He played a transgender Irish woman in the comedy-drama Breakfast on Pluto (2005), which earned him a Golden Globe Award nomination.