Claudius was seen as something of a weakling by his nephew, the Emperor Caligula. As a result he was able to survive his nephew's reign, and his nephew would at times turn to him for advise.
After the robe used by Jesus Christ before his crucifixion disappeared Caligula went to Claudius to see if he could determine the robe's whereabouts. Caligula believe the robe had magic powers and would make him immortal.
Claudius watched as his nephew slipped further into insanity, declaring himself to be a god and trying to resurrect a prisoner after killing him. When he lowered the pay of the Praetorian Guard and made their working conditions worse the Guard became quite angry. They had enough when ordered to kill Demetrius, and instead killed Caligula.
The Guard then proclaimed Claudius Emperor. A short time later at the Imperial Palace Claudius informed the assembled people that he had played a weakling to survive under his nephew's rule. He said that unlike his nephew he did not consider himself a god nor was he likely to become one anytime soon. Claudius said going forward he would rule to the best of his abilities. He gave Demetrius his final orders as a Roman Tribune, to go to Peter and to tell them that as long as the Christians didn't plot against the Emperor he would leave them alone.