This is the Emperor of the Imperium and the leader of the Sardaukar.
Corrino is a prideful guy. We would be, too, if we were emperor of the entire universe, like him. Unfortunately for the Emperor, Paul decimates his Sardaukar with a force of Fremen soldiers. With no other option, the Emperor negotiates for Paul to marry his daughter Irulan, and then he's banished to Salusa Secundus to live out the rest of his days Napoleon-style.
The Emperor is mentioned throughout the novel, but we only get to know him in a few choice scenes. Perhaps the best of these are the excerpts introducing each chapter. Here, Irulan describes him as a man radiating immense power in everything he does. But she also notes him to be:
[…] a man fighting constantly to escape the bars of an invisible cage. You must remember that he was an emperor, father-head of a dynasty that reached back into the dimmest history. (33.Intro)
Corrino might serve to foreshadow Paul's own future. Although Paul defeats the Emperor and assumes his power, he might just have trapped himself in that cage as well. Only one way to find out: you'll have to read those sequel novels.