Answer
Caligula was a great-grandson of Livia Drusilla. Livia was a Roman empress who was the third wife of the Roman emperor Augustus. She was also the mother of the Roman emperor Tiberius. Caligula was the son of Germanicus, who was the nephew of Tiberius. Germanicus was poisoned by Livia and her lover, the Roman general Sejanus. Caligula was later adopted by Tiberius and became emperor in AD 37.