Digimon Emperor

Digimon Emperor is first antagonist of Digimon Adventure 02. He and Ken Ichijouji are same person.

In Confession, Mysterious Man has the ability to change his form into that of Ken as a 14 years old version of the Digimon Emperor.

Digimon Adventure 02
In Enter Flamedramon,

In The Digiteam Complete,

In A New Digitude

In Iron Vegiemon,

In Old Reliable,

In Family Picnic,

In Guardian Angel,

In Ken's Secret,

In The Emperor's New Home,

In The Captive Digimon,

In Storm Of Friendship,

In The Good, The Bad, and The Digi,

In Big Trouble in Little Edo,

In 20,000 Digi-Leagues Under the Sea,

In Run Yolei Run

In An Old Enemy Returns,

In The Darkness Before Dawn,

In The Crest of Kindness,