Alexander Tulloch Macqueen (born 30 November 1973) is an English actor and writer. He has appeared on television, film, and radio in the UK in productions such as Holby City, Hut 33, Peep Show, The Thick of It, Keeping Mum, Fate: The Winx Saga, and The Inbetweeners. He also guest-starred in The Durrells in series 4.

Alexander Tulloch Macqueen was born on 30 November 1973 in Epsom, Surrey.^{[citation needed]}

He was educated at St John's School, Leatherhead, from 1990 to 1992 and left to receive a first in English literature at Collingwood College at Durham University.

He went on to study for a MPhil degree at Pembroke College, Cambridge, graduating in 1998.

Macqueen played sarcastic consultant anaesthetist Keith Greene in 75 episodes of Holby City between May 2005 and July 2010. He appeared as the Rt Hon Julius Nicholson, Baron Nicholson of Arnage, the bawdy and persistently peckish "blue-skies advisor" to the Prime Minister in political satire The Thick of It and also played Sir Jonathan Tutt, the British Ambassador to the UN, in the spin-off film In the Loop; both were directed by Armando Iannucci. He also acted in the Comic Relief special of Mr. Bean in 2007 as a vicar. He played Kevin Sutherland in E4's comedy The Inbetweeners. In 2010, he starred as Howard, an anti-speed bump community campaigner in two episodes of Outnumbered on BBC One.

He appeared in the Comedy Central / BBC collaboration Kröd Mändoon and the Flaming Sword of Fire, in which he played Barnabus, the sidekick to the Chancellor Dongalor, played by Matt Lucas. He starred as Roy Tunt in The Hide, which premiered on FilmFour in February 2009. He won the award for Best Actor at the Marbella Film Festival in 2009 for this role.^{[citation needed]}

Macqueen acted in a series of videos on YouTube as Clive Rudloe, a character who claims to be "the world's number one DJ". The videos are spoofs created by real-life DJs Above and Beyond. In late 2009, he starred in several episodes of The News at Bedtime on BBC Radio 4, in a variety of supporting roles. In 2010, he appeared as the publisher Malcolm Dodds in Woody Allen's You Will Meet a Tall Dark Stranger. That year, he also had a small role in the comedy film Four Lions. In 2011, he was in "The National Anthem", an episode of the anthology series Black Mirror.

In 2012, he appeared in a Doctor Who spin-off UNIT: Dominion, published by Big Finish Productions, in a role described as "the Other Doctor" who is revealed to be the Doctor's long-term adversary The Master; the storyline establishes that Macqueen's Master is intended to be from a point between the Masters portrayed by Eric Roberts and Derek Jacobi. He reprised this role in 2014 for Dark Eyes 2, Dark Eyes 3, Dark Eyes 4 and again in 2016 alongside Geoffrey Beevers, who had played an earlier incarnation of the Master, in The Two Masters. In 2021, Macqueen returned to the role in Masterful, a story published to celebrate the Master's 50th anniversary. He again returned to the role in The Stuff of Legend, an audio drama which was also staged as a live theatrical performance at Cadogan Hall in September 2024.