Alexander Slater is a minor antagonist in Resident Evil: Extinction. Slater (portrayed by Matthew Marsden) is an Umbrella executive and second in command of the company's Science Division under Dr. Sam Isaacs. However, he takes his orders directly from Albert Wesker - Umbrella's chairman - who orders Slater to report on the doctor's activities. He despises Isaacs and knows that the doctor has gone behind Wesker's back as he researches in the domestication of the undead and the monitoring of Project: Alice.
When Dr. Isaacs is bitten and infected by one of his mutated zombies, he administers several vials of anti-virus to stabilize his infection. Slater informs Isaacs that Umbrella will no longer tolerate his rogue actions and executes him by shooting him in the head. However, Isaacs has started to mutate exponentially and survives the gunshot, gets back up and extends his fingers into thick, writhing tentacles that impale Slater through the eyes and mouth, killing him.