He is married to Francine Smith and has two children, his eldest child is Hayley Smith (though one episode implies she may not be his child), who often opposes his views, and Steve Smith, a geeky child who is Stan's favorite, despite many of Steve's nerdy characteristics. Many episodes revolve around Stan trying to make Steve more manly but often times his efforts fail. He also has a Cherokkee half-brother named Rusty Smith.
Even though he is muscular, he is also a bit fat, though he appears more fit in a suit. Later episodes have diminished his gut making him much more fit.
Depending on the episode, Stan is either intelligent and uses his wisdom to save the day or stupid and arrogant forcing him to be humbled.