Bell is stuck in the B-Universe, he has traveled between dimensions so many times, that his atoms would react like an atomic bomb if he were to try to cross back over. He aids the Fringe Division in any way he can to help them protect his and their universe. There’s a war coming, and that is why him and Dr. Bishop conducted their human drug (cortexiphan) trials, in an effort to create “super soldiers” to protect our universe from a coming threat. In his absence, he has left Nina Sharp in charge of Massive Dynamic.
American actor Leonard Nimoy plays William Bell in the TV serie.