(Capcom's primary storyline)
ε was developed in 1998 as a t-Virus strain more likely to create Tyrants by limiting brain damage. The first ε mutant was the Tyrant (T-002 Model). An airborne form of the virus was released from the Tyrant's body during injection into the host, a strong adult male prisoner, as a result of an accident caused by the Queen Leech. It eventually contaminated the facility's water supply and infected the above-ground mansion staff, becoming a transdermal strain once infected humans became Zombies. One ε mutant strain discovered in the mansion exhibited the V-ACT effect, known to transform Zombies into fast and clawed Crimson Heads.
"ε" and its own modified variants are the most commonly-occuring t-Viruses in the series. Most Zombies in Resident Evil; Resident Evil 2; Resident Evil 3: Nemesis; Resident Evil Outbreak and Resident Evil Survivor are infected with it, though not necessarily all.