(Covers information from Anderson's universe)
The Licker is a biological weapon created by directly injecting the T-virus into live human tissue.
The first known Licker was a cluster developed within The Hive, one of the Umbrella Corporation's bio-weapons laboratories. One Licker was released from confinement to hunt down Umbrella's "Sanitation" taskforce by the Red Queen to prevent an outbreak of the virus spreading beyond the laboratory itself. The Licker killed Spence at the train platform, and after feeding on his body, mutated into a new form. The Advanced Licker then proceeded to follow Rain; Janus Prospero; Matt Addison and Chad Kaplan. The creature threw Kaplan straight out of the train, likely killing him, and scratched Addison, infecting him with a mutant strain of T-virus. Matt and Janus killed the Licker as they escaped from the train.
In a second attempt to access The Hive, Umbrella inadvertantly released the Undead and a number of Lickers into Raccoon City. A number of these Lickers took shelter at Raven's Gate Church, where they were killed by Janus while hunting a group of survivors.
An animatronic model was created for the first Resident Evil film, with CGI enhancements and a tongue added in post-production. Another animatronic was created for Apocalypse, but special effects supervisor Alison O'Brien found it to be inadequate and switched to full CGI. This required the special effects team to examine meat at a marketplace to get the right texture and colour for what O'Brien described as a "flayed human".