Bob's got the power to perform a Fusion Dance with other people, with or without their consent. When he does, he takes from them their personality and memories. Whether or not the people live on inside his own mind varies from work to work. Generally speaking, this sort of thing kills the absorbee, although exceptions exist. Compare Mental Fusion, where both Alice and Bob are still alive, but a mental link is formed between them. See also: You Will Be Assimilated, Mega Manning, Tanks for The Memories, and Memory Gambit