Aleksandar Živojinović (Serbian Cyrillic: Aлександар Живојиновић, OC, born August 27, 1953) better known by his stage name Alex Lifeson, is a Canadian musician, best known as the guitarist of the Canadian rock band Rush. In the summer of 1968, Lifeson co-founded the band that would become Rush. Other co-founders are friend and drummer John Rutsey, bassist and lead vocalist Jeff Jones, and Jones's successor, current front man Geddy Lee a month later. Lifeson has been an integral member of the band ever since.

For Rush, Lifeson plays electric and acoustic guitars as well as other stringed instruments such as mandola, mandolin, and bouzouki. He also performs backing vocals in live performances, and occasionally plays keyboards and bass pedal synthesizers. Like the other members of Rush, Lifeson performs real-time on-stage triggering of sampled instruments, concurrently with his guitar playing.