Ben Roethlisberger spent most of his career beating the Cincinnati Bengals -- but it turns out, The Tiger King is still a huge fan!!!
TMZ Sports has confirmed ... Joe Exotic has written a letter to Big Ben from prison, asking the Pittsburgh Steelers star for his autograph.
Exotic's lawyer, John M. Phillips, tells us the 59-year-old penned the note just recently.
In his letter, Exotic told the future Hall of Famer that he needed a signature from Ben so he could gift it to his stepson for a birthday present.