He spent years as a political prisoner when he was young. As a result, he dedicated his terms as secretary-general to fighting corruption in the government.
After the Ganymede incident, Chrisjen Avasarala debriefs him on the activities surrounding it including Venus. Chrisjen Avasarala privately refers to him as "The Bobblehead." The nickname reinforces the fact that Esteban acts strictly as a man influenced by his underlings as opposed to one that has any meaningful thought or action of his own.
Both the Eros incident and the Ganymede incident occured during Sorrento-Gillis's term, and prior to the election to his office he was massively criticized for turning a blind eye to rogue corporate entities such as Protogen and Mao-Kwikowski Mercantile. He lost his reelection to Nancy Gao.