Tiberius accepted his position and title as emperor with apparent reluctance. Though he proved a capable and efficient administrator, he could not match his predecessor's extraordinary energy and charisma. Roman historians described him as morose and mistrustful. With a self-deprecation that may have been entirely genuine, he encouraged the cult to his father, and discouraged his own. After much wrangling, he allowed a single temple in Smyrna to himself and the "genius" of the Senate in 26 AD; eleven cities had competed – with some vehemence and even violence – for the honour. His lack of personal "auctoritas" allowed increasing praetorian influence over the Imperial house, the senate and through it, the state. In 31 AD, his praetorian prefect Sejanus – by now a virtual co-ruler – was implicated in the death of Tiberius' son and heir apparent Drusus, and was executed as a public enemy. In Umbria, the Imperial cult priest ("sevir Augustalis") memorialised "the providence of Tiberius Caesar Augustus, born for the eternity of the Roman name, upon the removal of that most pernicious enemy of the Roman people". In Crete, thanks were given to "the "numen" and foresight of Tiberius Caesar Augustus and the Senate" in foiling the conspiracy – but at his death, the senate and his heir Caligula chose not to officially deify him.