Aleksandar Živojinović (born 27 August 1953), known professionally as Alex Lifeson (), is a Canadian musician, best known as the guitarist for the rock band Rush. In 1968, Lifeson co-founded a band that would later become Rush, with drummer John Rutsey and bassist and lead vocalist Jeff Jones. Jones was replaced by Geddy Lee a month later, and Rutsey was replaced by Neil Peart in 1974, after which the lineup remained unchanged until the band's dissolution in 2018. Lifeson was the only member of Rush who stayed in the band throughout its entire existence, and he and Lee were the only members to appear on all of the band's albums.

With Rush, Lifeson played electric and acoustic guitar, as well as other various string instruments such as mandola, mandolin, and bouzouki. He also performed backing vocals in live performances and select studio recordings, and occasionally played keyboards and bass pedal synthesizers. Like the other members of Rush, Lifeson performed real-time on-stage triggering of sampled instruments. Along with his bandmates Geddy Lee and Neil Peart, Lifeson was made an Officer of the Order of Canada on 9 May 1996. The trio was the first rock band to be so honoured as a group. In 2013, he was inducted with Rush into the Rock & Roll Hall of Fame. Lifeson was ranked 98th on Rolling Stone's list of the 100 greatest guitarists of all time and third (after Eddie Van Halen and Brian May) in a Guitar World readers' poll listing the 100 greatest guitarists.

The bulk of Lifeson's work in music has been with Rush, although Lifeson has contributed to a body of work outside the band as well, including a solo album titled Victor (1996). Aside from music, Lifeson has been a painter, a licensed aircraft pilot, an actor, and the former part-owner of a Toronto bar and a restaurant called The Orbit Room, which closed in 2020.