Tommy Oliver is first introduced in the Mighty Morphin Power Rangers five-part episode "Green with Evil" as a new student at Angel Grove High School. Unlike other Power Rangers, his outfit includes a golden shield armor and two golden armbands. After he spars with Jason Lee Scott (Red Power Ranger) in a martial arts tournament, he catches the eye of both Kimberly Hart (Pink Power Ranger) and the evil witch Rita Repulsa. Rita decides to enchant Tommy to be her loyal servant, granting him the Dragon Power Coin to give him the power to transform into the Green Power Ranger, possessing the Dragon Shield, which makes him stronger than the other Power Rangers, and armed with the Dragon Dagger and the Sword of Darkness. She orders him to destroy the Power Rangers and their guardian Zordon so she may be able to conquer the Earth unopposed. He succeeds in his mission, dispatching of Zordon, destroying the Power Rangers' Command Center, and infecting the robot Alpha 5 with a computer virus, leaving the Rangers defenseless against attacks, but they are still able to ward him off with the Megazord. With the return of Goldar's wife Scorpina, the two wreak havoc in Angel Grove, leading the Power Rangers to use the Megazord once more, only to be attacked by Goldar, Scorpina, and the Green Ranger at once, putting the Megazord out of commission when it is thrown into the Earth's core. After this battle, the Power Rangers discover that their foe is none other than their classmate Tommy. After Tommy escapes, he uses the Dragon Dagger to summon the Dragonzord to attack the city. Zordon is revived and reveals the Power Rangers' Dinozords have been restored by the Earth's lava, allowing them to counter the Dragonzord's attack. The Red Ranger is then able to battle the Green Ranger one-on-one, and destroys the Sword of Darkness, freeing Tommy from Rita's spell. Zordon then offers Tommy a part on the team to atone for his misdeeds, and he agrees.
During his time with the group, Tommy recognizes Kimberly's feelings, having broken her heart while he was under Rita's spell, and he now begins to show affections for her. However, Rita's plan to use the evil Green Candle to get revenge on Tommy for leaving her employ, weakens Tommy, just as Kimberly returns his affections. Tommy is captured by Goldar and kept imprisoned in the Dark Dimension as the Green Candle burns down, draining him of his strength. Tommy is ultimately freed, but not before the Green Candle burns through completely. His powers nearly gone, after using them in one final battle with a powerful monster, he decides to give the Dragon Coin to Jason, permanently preventing Rita from attaining its power once more. Tommy then leaves Angel Grove to recover from the endeavour.
After Rita kidnaps all of the parents of the students of Angel Grove High School, the Power Rangers are forced to pay her ransom with their Power Coins, preventing them from using their powers. When they are double-crossed, and Rita acquires the Dragon Dagger by enchanting Billy Cranston, all seems hopeless, but Jason reveals he still has the Dragon Power Coin. The group finds Tommy once more, and with help from Zordon, Tommy is able to morph into the Green Ranger and retrieve the Power Coins and Dragon Dagger. However, his powers are now unstable and he requires constant energy boosts from Zordon in order to maintain his place as the Green Ranger. With the arrival of the evil Lord Zedd in season 2, the other Power Rangers are given new Thunderzords to battle his stronger monsters, but because of Tommy's link to Zordon, the Dragonzord cannot be empowered into a new form. With this knowledge in mind, Lord Zedd sends several energy draining monsters to steal the Green Ranger's powers to the point where Zordon can no longer safely maintain himself and the Green Ranger. This culminates in the attack of the monster Turbanshell, who drains Tommy of his Green Ranger powers for good, trapping everyone in the Otherworld dimension, while charging the Dark Crystal to power Lord Zedd's evil Dark Rangers to attack the Earth. Tommy uses the last of his powers to destroy the Dark Crystal, ending the reign of terror of the Dark Rangers and allowing the others to defeat Turbanshell. With his powers gone, Tommy leaves Angel Grove, again, spending time at his uncle's lakeside cabin.