Henry Kuttner 
A Million Years to Conquer [The Creature from beyond Infinity] 

The story concerns Ardath, the last member of a dying race from a doomed planet, his ship downed on Earth millions of years in our past, his mission to wait until intelligent life develops, then select the brightest of the race in various time periods, breed them into a super race, and recreate the splendour of his own long-lost civilisation. Classic pulp fiction.