Diabolico was one of four demons released from an underground tomb. In his Queen's absence, Diabolico took command of the evil forces. His plan is to destroy Marinerand restore what he believes to rightfully his - the palace Mariner Bay was built on. Diabolico's time ran out, and he was unable to destroy Mariner Bay before the Queen's arrival. Out of desperation, he battled the Rangers himself, and was destroyed by the Lightspeed Solarzord.
After being betrayed by Olympius, Vypra and Loki resurrected Diabolico. He rejoined the team, plotting to overthrow Olympius and regain his star power. Diabolico turned on the Queen when she killed his friend Loki, and was killed himself when Olympius took control of his mind to battle the Rangers. Diabolico returned one last time as a spirit to pull Queen Bansheera into the demon shadow world.