The Joker Undead is later revealed to be the true identity of Hajime Aikawa aka Kamen Rider Chalice. The Black Joker represents Death in the Battle Fight and were it to win, all life on Earth would be ended.
Kamen Rider Blade
After sealing the Giraffa Undead, Hajime loses control and the Joker surfaces within him, with the Stone of Sealing creating an army of Dark Roaches to eliminate all humans.
Hajime pleads with Kenzaki to seal him, but Kenzaki manages to find another way to defeat the Joker by mutating into one through excessive use of King Form transformation, saving Hajime and prolonging the fight, as well as averting destruction indefinitely. However, this also forced the two to never see each other again or else they would be forced to fight when they meet again.
Kamen Rider Decade
The Joker Undead reappears in the World of Blade when BOARD head Hajime Shijo uses the completed Joker Rouse card to evolve into one. However, he was destroyed by Kamen Riders Blade and Decade.
Kamen Rider × Super Sentai: Super Hero Taisen