Who is Glossu Rabban-Harkonnen from Dune and what is their importance?

Glossu Rabban-Harkonnen is Baron Vladimir's Harkonnen's older nephew. He is described as a dim-witted, overweight "Beast". As a result, he has fallen out of favor with his uncle and has been replaced as his successor by younger brother Feyd-Rautha.

After the Harkonnen/Sardaukar coup d'état, Rabban is restored to power as governor of Arrakis, and he is ordered to "squeeze" the population. Knowing this would embitter the people, the Baron is certain that he will be able to replace him.