Thanos Robertson is Fat Albert's father. Appearance-wise, he is fat just like his son and has an identical haircut. He also has a thick black mustache.
In the episode "What Does Dad Do?", it is shown he has a job lifting boxes in a factory, and that restoring balance to the universe by wiping out half of it is a side-project.
He is voiced by Lou Scheimer, but in "What Does Dad Do?", he was voiced by a different voice actor. Most likely Josh Brolin, because after all, he is Thanos.