Book For We Are Many — Dennis E. Taylor

Bob Johansson didn't believe in an afterlife, so waking up after dying in a car accident was a shock. To add to the surprise, he is now an intelligent computer and the controlling intelligence of a von Neumann probe.
Bob and his copies have been dispersing from Earth for 40 years in search of habitable planets. But this is the only part of the plan that is still intact. A system-wide war has wiped out 99.9% of the human race; a nuclear winter is gradually making Earth uninhabitable; a radical group wants to finish off the remnants of humanity; Brazilian space probes are still around, still trying to blow up their competitors; and the Bobs have discovered an alien species that views all other life as food.
Bob left Earth expecting a life of exploration and blissful solitude. Instead, he became the sky god for a primitive local species, the only hope for humanity to find a new home, and perhaps the only thing that could prevent every living thing in the local realm from becoming dinner.