X. Wild Force
The Power Rangers use their powers to defeat the forces of the Orgs, led by one Master Org. As Cole was fond of animals, he was shocked to discover that the Orgs were heartless creatures. As the series continues, he finds the truth about his real parents: his parents, Richard and Elizabeth Evans, were professors at Turtle Cove University, along with a family friend, Viktor Adler. When they were sent to the jungle for research, they discover the remains of Master Org, in which a jealous Adler consumes in order to exact revenge on Richard, who had proposed to Elizabeth before he could. However, Adler goes insane, and kills both Richard and Elizabeth. For a while, their newborn son, Cole, was also presumed dead.
The annual team-up episodes saw the Wild Force Rangers team up with the Time Force Rangers in order to stop three mutant Orgs (the Mut-Orgs) from polluting the Earth. It also featured the first time when a former villain teamed up with the Rangers to face the enemy. These episodes are special as it contained numerous references to various longtime fans of Power Rangers. Fans generally consider this teamup one of the best, due to the fact that the episode was written by a member of the fandom who was later hired to write for Wild Force, and the fact that the teamup brought closure to several plotholes in Time Force.
In addition to the annual team-up episodes, Power Rangers: Wild Force also had a special episode commemorating it as the tenth incarnation, by having Cole team up with the nine Red Rangers before him, (in order of incarnations, Jason Lee Scott, Aurico, Tommy Oliver, T.J. Johnson, Andros, Leo Corbett, Carter Grayson,Wes Collins and Eric Myers), in order to defeat the Machine Empire one final time. This was known as Forever Red.”
-Taken from: http://powerrangers.wikia.com/wiki/Wild_Force