There weren't enough fighters in EA Sports UFC 2, at least not until Joe Rogan was added to the roster. While Rogan tends to be on the sidelines announcing the fights, sometimes the guy just have to rip off his shirt and join the fight.
That's probably why he took to Instagram (via BJPenn) to reveal the 'secret' code to unlock him as a player in the game. Now that he's revealed it, it's not so secret any more.
To access Rogan, your version of UFC 2 needs to be updated to the latest title update. Once your game is updated, enter the 'secret' code while on the game's main screen.
Here's the code on both the PS4 and Xbox One:
PlayStation 4: Up, Up, Down, Down, Left, Right, Left, Right, Circle, X and Options
Xbox One: Up, Up, Down, Down, Left, Right, Left, Right, B, A and Menu.
Yep, it's basically the Konami code, with a couple extra buttons tacked on.
You can check out the full roster for the game here or watch Conan O'Brien take on Conor McGregor and get wrecked.