Sir Derek George Jacobi CBE (born 22 October 1938) is an English actor and stage director.

A "forceful, commanding stage presence", Jacobi has enjoyed a highly successful stage career, appearing in such stage productions as Hamlet, Uncle Vanya, and Oedipus the King. He has twice been awarded a Laurence Olivier Award, first for his performance of the eponymous hero in Cyrano de Bergerac in 1983 and the second for his Malvolio in Twelfth Night in 2009. He also received a Tony Award for his performance in Much Ado About Nothing in 1984 and a Primetime Emmy Award in 1988 for The Tenth Man. His stage work includes playing Octavius Caesar, Edward II, Richard III, and Thomas Becket.

In addition to being a founder member of the Royal National Theatre and winning several prestigious theatre awards, Jacobi has also enjoyed a successful television career, starring in the critically praised adaptation of Robert Graves's I, Claudius, for which he won a BAFTA; in the titular role in the acclaimed medieval drama series Cadfael, and as Stanley Baldwin in The Gathering Storm.

In 2003, he was involved with Scream of the Shalka, a webcast based on the science fiction series Doctor Who. He played the voice of the Doctor's nemesis the Master alongside Richard E. Grant as the Doctor. In the same year, he also appeared in Deadline, an audio drama also based on Doctor Who. Therein he played Martin Bannister, an ageing writer who makes up stories about "the Doctor", a character who travels in time and space, the premise being that the series had never made it on to television. Jacobi later followed this up with an appearance in the Doctor Who episode "Utopia" (June 2007); he appears as the kindly Professor Yana, who by the end of the episode is revealed to actually be the Master.

In 2013, Jacobi joined Ian McKellen in the ITV sitcom Vicious as Stuart Bixby, the partner to Freddie Thornhill, played by McKellen.

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