H. Beam Piper 
Space Viking 

When his wife is murdered on his wedding day, Lucas Trask launches himself on a quest for revenge. Using his personal fortune, he buys a spaceship and becomes a Space Viking, raiding worlds while hunting for his wife’s killer. But raiding is not his destiny, and he gradually becomes a trader, starting to build a galactic empire. Before he can achieve his new goals, however, he must still deal with his wife’s killer.