Commodus followed Caligula.
Roman imperial history is inherently biased and not necessarily very accurate.
The early months of Caligula's reign actually were pretty universally praised - and then his popularity cratered. There are two basic theories for what happened:
Caligula went mad and did every depraved thing he was accused of.
The patricians realized that Caligula was actually going to extend the power of the emperor even further than his predecessor, Tiberius, had and turned on him with a vengeance.
Again, remember, the history of Caligula's reign was mostly written by the descendants of the people who plotted to assassinate him - so of course they weren't about to make him look good.