Tony Masters was the husband of Cheryl Masters and brother-in-law of John Constantine. Tony and John did not like each other.
Tony was involved with the Resurrection Crusade, and completely relied on them when Gemma disappeared. He left the church shortly after.
Over 10 years later, Tony was duped the demonness Rosacarnis. She used him to murder Cheryl. When Gemma confronted him with it, he decided to kill himself.