|The US cover of Ilium (I like it better than the UK one)|
Ilium and Olmypos are two sci-fi novels by Dan Simmons (author of the ) that form a duology. The plot of this series is very complex (some would say convoluted), and many things are left unexplained at the end. Still, the writing is masterful and the story is engrossing. The plot involves posthumans that experimented with technologies that allowed them to travel to alternate universes - however, this led to their downfall, as they opened portals that led Bad Things™ into their home universe. One of these beings, Prospero (based on the character in Shakespeare's The Tempest) wasn't quite so evil, and saved many of the posthumans by transforming them into Greek gods. They use incredibly advanced technology to simulate the divine powers such gods were supposed to have, and play their respective roles in the story of the Trojan War, taking place in an alternate universe. Meanwhile, the remaining humans on earth have fallen into a primitive and ignorant lifestyle, but still enjoy a high standard of living due to the robots and the mysterious Voynix that serve them. There are also sentient machines called Moravecs that live in the outer solar system, and investigate these goings - on.
Of course, this is just a brief overview, and there are many more subplots, characters, races, and locations in the books.
Standing in the Battledome:
The character from this universe most often used in the OBD is Achilles, the legendary Greek warrior who has been enhanced by the gods with the ability to move at relativistic speeds, have class 100+ strength, durability to take city/mountain-busting attacks easily, and to be immortal. Despite his obvious brokeness, he's far from the most powerful character in the story, as various gods and aliens are universal threats. The strongest being in the Illium/Olympos universe is known as The Quiet, and is hinted to be omnipotent (but not omnipresent). Due to lack of feats and general information, The Quiet is rarely used in the OBD (AFAIK it hasn't been used at all so far).