(Capcom's primary storyline)
Dominant species Plagas are an artificial subspecies of the Plaga parasite, mainly characterized by the extreme mutations they can trigger in their hosts and their ability to bond with a host without compromising their higher thought processes, giving the host a greater degree of control over them. They were experimented on for B.O.W. research by companies such as TRICELL.
Dominant species Plagas are named as such because they are not susceptible to the ultrasound-based orders that regular, "subordinate" Plagas follow. Unlike regular Plagas, dominant species Plagas did not affect the host's consciousness, allowing for higher levels of cognitive thought and speech. However, this also meant that hosts of a dominant species Plaga were impossible for the likes of Osmund Saddler to control, forcing those seeking to weaponize the parasites to choose their hosts with extreme caution.
As shown with Jack Krauser, Ramon Salazar, and Bitores Mendez, it seems that the host is responsible - at least with Los Iluminados' version - for triggering the parasite's sudden, dramatic mutation and mutilation of the host body. Since no two individuals infected with a dominant species Plaga appeared to exhibit the same transformation, it is believed that the mutations are affected by either the host's immediate environment, or by the host's will at the time. An example is Ricardo Irving's transformation into a massive aquatic beast after injecting himself with a dominant species Plaga after the parasite adapted to the immediate environment.
In the case of Irving and Salazar, the human host's body also gets partially enveloped in a fleshy cocoon, often leaving their right arm exposed as well as the left sides of their face fused with part of the membrane while connected to a far larger beast-like Plaga form, as well as protected by the beast's "mouth." However, of the two, only Irving's transformation was the direct result of his own injected Plaga, as Salazar's transformation was the result of him and his remaining Verdugo guard fusing with the Queen Plaga.