An interesting "demigod" I had in my mind was just a scientist from the future... who stumbled upon the Demigod era in a time machine, bringing his vastly superior technology to the realm... all of the locals thought his technological devices were magic... and thus they worpshipped him as a demigod... he then gets attacked out of fear for his power by local bringands... utilizing his technology to defend himself.. he succeeds... and as the gods above watch, he gets invited to the pantheon.
He's basically a scientist form the future, who timewarped into the past... the Demigod era. He's no fighter, but he's extremely brilliant and intelligent, capable of making anything from almost nothing. He uses his smarts, technology, and cunning in battle. I would assume he would be a general... fielding an army of sysnthetic soldiers to fight on his behalf to protect himself. I can't decide if he would be a more like a Doc Brown "good scientist" from back to the future, or more of an evil megalomanical bad scientist I'd leave that up to GPG and Stardock to decide.
I can't think of a name for this "demigod" but I think it would be a very unique and awesome addition to the game.