Complex sentence: His younger brother, Hiranyaksha was slain by Varaha, one of the Avatars of Vishnu and angered by this, Hiranyakashipu decided to gain magical powers by performing a penance for Lord Brahma.
Split into simpler sentences: His younger brother, Hiranyaksha was slain by Varaha, one of the Avatars of Vishnu. Angered by this, Hiranyakashipu decided to gain magical powers by performing a penance for Lord Brahma.