He has all the accoutrements of a demonologist - the robe covered in sigils, a sword so heavy with runes that it bends, magical Octagrams and so on, but there is one detail missing: about seventy years. He's fourteen. And acne-scarred. His grandfather tried for years to summon a Succubus but all he ever got was a Neuralger - a demon that comes and has a headache at you.
His purposes for summoning a demon are summed up thusly: he wants three wishes. And he wasn't messing about either - he wanted to rule the world, live forever and have the most beautiful woman in the world.
Rincewind fell through the summoning by mistake (he was trapped in the Dungeon Dimensions following a series of events detailed in Sourcery) and was expected to deliver these wishes. Obviously he couldn't do this, but each time he snapped his fingers, something happened that was broadly in line with these wishes. To wit:
- Ruling the world: he was given tribute by the Tezuman but then they wanted to sacrifice him;
- Meeting the most beautiful woman in the world: this was Elenor of Tsort, and when they arrived in her time (again not to their liking) they inadvertently ended the Tsortian War.
- Living forever: he (along with Rincewind) was sent to the beginning of all time and then would have had to live for eternity. This didn't appeal, hence the deeply intelligent rewriting of the spell mentioned above.
The arbiter of all this was not the powerfully inept Rincewind, but the rather more powerful and malevolent Duke Vassenego, one of the supreme demon lords of Hell. He had his reasons for doing all of this, chief amongst which was his plotting to supersede Astfgl as the ruler of Hell.
After all their adventures, Eric and Rincewind ended up in Hell, from which they managed to escape as Vassenego's plan came to fruition.
Eric gave his address as 13 Midden Lane, Pseudopolis, Sto Plains, The Discworld, On Top of Great A'Tuin, The Universe, Space, nr. More Space, but his current whereabouts are unknown. Presumably he's still living, as Duke Vassenego let them go in order to a) encourage humanity to continue to stupidly dabble in demonology and b) to really annoy Astfgl.
It may be the case that he is a spoof of Michael Moorcock's fantasy creation, the necromancer Elric, who is a necromancer/warrior in Moorcock's series of straight, if high-camp, fantasy novels. He is handicapped by his being a weak and enfeebled albino, whose energy fails rapidly if not sustained by eldritch drugs or the proximity of the dread hell-sword Stormbringer. (Kring in the Discworld-view) He regularly calls for the support and patronage of the Chaos demon/god Arioch to assist him. Arioch sometimes obliges. Elric is the first manifestation of the Eternal Champion, doomed to be continually reincarnated down the echoing corridors of time and space to serve whichever threatened civilization requires his services.