The Star King: Jack Vance

Book I of Demon Princes. All his life, Kirth Gersen had had a single dream -to rid the galaxy of the five Demon Princes, the evil beings who had killed his parents and brought terror to the Oikumene. Trained for vengeance, Gersen learnt to crave their blood with every fibre of his being. Attel Malagate was the first name on his death list: a Star King with a fearful lust for power, he roamed the Beyond in human form. But his humanity was only skin deep. Underneath was a cruelty and a barbarism that would shock even the most depraved and savage of humans...