Gaius Julius Caesar Germanicus, nicknamed Caligula or "little boots" by the troops of his father Germanicus, became Emperor of Rome in A.D. 37. The young Caligula enjoyed widespread popularity for a brief period at the beginning of his reign, but soon his behavior became increasingly autocratic and megalomaniacal. Following his assassination on January 24th in A.D. 41, the Senate passed official sanctions against his memory (damnatio memoriae) and ordered the destruction of his public images. As a result, only very few of his portraits survive.
For a recent discussion of the portraiture of Caligula see pp. 96-125 in Varner, ed., From Caligula to Constantine, Tyranny & Transformation in Roman Portraiture. For a related cameo portrait of the emperor, slightly re-worked, see no. 296 in Vollenweider, Deliciae Leonis, Antike geschnittene Steine und Ringe aus einer Privatsammlung.