He was a rouge Time Lord imprisoned on a jungle planet by Rassilon. His regenerations were taken.
The 1st Doctor,Ian And Barbara encountered him on a jungle planet in the Quarex galaxy. He was trying to use the planets power from the core to power his prison ship. The blast would shrivel the planet. His plans were foiled by the 3 when they used the power to melt the ship. He attemped to shoot them as they fled to the Tardis. They escaped leaving him trapped.
A cyberman pod,CYBO from Mondas crashed there. He took control of The Cybermen and their pod. He escaped the planet using the pod.He tried to kill the 2nd Doctor who with Jamie and Zoe were on Delta Magnas. The Cybermen attacked under his order but the Doctor tricked them into falling into the swamp. He set the pod to explode. The blast would wipe out 50 miles. Upon fleeing through the swamp a beast jumped out the swamp and pulled him under. The Doctor managed to stop the pod exploding.
He survived this encounter and escaped using the pod. Not knowing how to properly use it he crashed. He ended up in Dalek custody on a space station. He helped create a power source for their doomsday weapon. When he relised they would kill him he released the 5th Doctor who had been captured. They went through the vents and tried to sabatoge the weapon but were seen. The Doctor escaped but he was captured. He was taken to Dalek command where he pleaded for his life. After they said exterminate he ran at the Supreme but was shot 3 times.
He managed to somehow regenerate but his soul was transferred into a Dalek. He blaimed the 6th Doctor and went to kill him .The Doctor led him up a mountain. Up there the Doctor put a charge on his back and rolled him down.A few meters down it exploded sending him toppling over and of the edge seemingly ending him for good.
He once again encountered the Doctor in his 7th regeneration this time trapped as a Human on Earth. The Doctor and Ace fought him in a house of horror at an amusment park. He used the animatrons to attack. The 2 defeated them and found him in the control room. He attempted to blast them but Ace used her bat to knock him unconscious. He was then arrested.
During the Time War he was brought to Gallifrey to fight but instead he joined the Daleks. The 8th Doctor met him in battle and in a moment of pure anger he shot him 5 times then kicked him into a pit where during regeneration he was engulfed by fire and killed.