^Since Devil May Cry 3 has been and gone, I have no regret in informing you that Arkham and Jester are the same person. Arkham used the guise of Jester to lure Dante deeper into the Teminigru<sp>, not to mention he used Jesters form to overwhelm the already exhausted twins and open the hell gate - Jester was merely a disguse for Arkham so he could execute his plan.
When Arkham dies, Jester dies with him ^^