(Covers information from Anderson's universe)
Warner was a Umbrella special forces commando.
Warner entered the mansion with the commando team when they were looking for Alice and Spence Parks. Later, Alfonso was the one guarding the prisoner Matt Addison. Alfonso and "Twelve" carried the equipment needed to shut down the Red Queen.
Warner had a hard time keeping cool under pressure, as shown when he entered the Red Queen's chamber. As the first to notice the laser defense grid, he successfully dodged the first beam that killed Twelve and the Medic. However, as he jumped to avoid a second beam heading for his feet, it unexpectedly rerouted and headed for his waist instead, bisecting Warner and slicing him in two.
Although only credited as "Commando #2", a scan by the Red Queen identifies him as "Warner".