Digimon Emperor

The Digimon Emperor was the main antagonist for about 1/4 of the Digimon Adventure season 2. His real name is Ken Ichijouji. He was once a DigiDestined and partnered with Wormmon. At first he thought that Digimon were nothing but programs in a computer so he decided to treat theme like slaves. He created these rings called Dark Rings that's similar to Devimon's Black Gears, and then upgraded them into Dark Spirials and the spires called Control Spires, in which they activate the Dark Rings and prevent others from Digivolve. The Emperor even created a monster called Kimeramon. When he finally figured out that what he was doing was wrong he tried to change his ways and decided (not right away) to join the other DigiDestined.

As Ken Ichijouji
Ken past was kinda vague but as the episodes went by he began to figure out his past. He helped the DigiDestined fight Arukenimon, Mummymon, MaloMyotismon and other evil Digimon. At the season finale it turn out that Ken and Yolei get married and have 3 kids. Ken also became a detective.