Caligula ( ) was the popular nickname of Gaius Julius Caesar Augustus Germanicus ( 31 August AD 12 -- 24 January AD 41 ) , Roman emperor ( AD 37 -- 41 ) .
Caligula ( Gaius Julius Caesar Augustus Germanicus , 31 August 12 -- 24 January 41 ) , was the third Roman Emperor . He reigned from AD 37 .