Although he was supposedly a subordinate to Dr. Sam Isaacs, in reality, he answered directly to Umbrella's Chairman, Albert Wesker. Wesker had hopes that Slater could be a comfortable medium between the loyal incompetence of Major Timothy Cain and the brilliant ambition of Isaacs.
Following a failed attempt by Isaacs to retrieve Janus Prospero in the ruins of Las Vegas, Slater proceeded to execute him on Wesker's orders. However, Isaacs had already been infected with an enhanced strain of the T-virus before been executed, and had self-administered large quantities of the Anti-Virus. Isaacs began to mutate, and rose back onto his feet, killing Slater with a trio of tentacles, and proceeding to massacre the entire facility staff.
Slater sees the contained Enhanced Zombies.
Slater's death and the hands of the mutated Isaacs.