William Bell (Leonard Nimoy) is the shadowy CEO of the Massive Dynamics corporation. Decades ago, he and Walter Bishop (John Noble) partnered in conducting questionable and dangerous experiments on human subjects that resulted in a lab assistant's death. Walter spent 17 years in a mental institution while Bell traveled into a parallel universe.
Olivia Dunham (Anna Torv), the most successful of Bell's and Bishop's experiments, ultimately meets him there along with Walter and his son, Peter (Joshua Jackson). Bell reveals several truths about the parallel universe, including the planned invasion into Olivia's world. He apparently dies when he uses his own body energy to send Olivia, Walter and Peter back to their own universe.
"It's OK, Walter. You always were as stubborn as a donkey with a nail in his head. "
"A storm is coming, perhaps the last and worst storm of all. And when it's over, I fear there will be little left of our world. The shapeshifters on your side are looking for someone to open the door between universes and if they find him, there will be no stopping them."