ideal for the part of the capricious Caligula. Peter O'Toole  ( Lawrence of Arabia ) was cast as the decadent Tiberius, while a young Helen Mirren  ( The Queen ) played Caligula's libertine wife, Caesonia . The great Shakespearean actor,  Sir John Gielgud ( Hamlet ) appeared as Marcus Cocceius Nerva, one of Tiberius's closest friends