It was Caligula, and it was just a little joke he made before his mind went kablooey. :’)
Yes, under the emperors the Senate was a joke (as witnessed by Caligula's horse being made a Senator). And even the office of the Emperor was for sale to the Praetorian guard. There was no “balance of powers”, there was only the absolute power of the Emperor, and the power of the Praetorian Guard to determine who would be Emperor.
And under an imperial system you also get effeminate “artists” like Nero, and vain madmen like Caligula. Neither of these two would ever have been elected Consul, and would most certainly not have been reelected.
The funniest thing I find about Roman history is how much the term “Dictator” has become a pejorative. The original concept was quite benign, and far better than any King. The Dictator was elected, and had absolute power only for a year or until the crisis was past. Cincinnatus was the ideal dictator, and the inspiration for the American city that bears his name and an association of the founders that gathered under the banner of his name.