Ruuvitar was dispatched with a contingent of Dominion soldiers to Shadowfen, presumably to find a way to force the Argonians out of the Alliance War. To this end, he searched for the Mnemic Egg, an ancient artifact that was the physical link between the Argonians and the Hist.
Ruuvitar's forces began their incursion into Shadowfen by using a Dremora named Lyranth and Hist Sap to create skin-stealer potion, an elixir that not only gave the drinker the appearance of their victim, but also their memories. This allowed the drinker to perfectly impersonate the victim. They began by killing and impersonating townsfolk in Stormhold, then moving on to high-ranking officials such as Vicecanon Hrondar. The Vestige was able to disrupt their operations in the city and also discovered Hrondar was an imposter. The Ebonheart Pact was now aware of the Dominion presence in Shadowfen and began mobilizing their forces.
Ruuvitar then sent his forces to secure the Hatching Pools, where Argonians eggs were laid beneath a Hist Tree before the hatched. Using the Mnemic Egg, he severed the link between the Hist and Argonians, causing nearly all the unborn Argonians in their eggs to die, save for a few that were saved by the Vestige and Keeper Uxith-Ei using an unknown ritual. Shortly after the slaughter, Pact forces arrived and recaptured the Hatching Pools.
After his success at the Hatching Pools, Ruuvitar desired to recreate the ritual he'd used on a larger scale, to prevent all Argonian births in all of Black Marsh. He moved the Mnemic Egg to the Ayleid ruin of Loriasel. There his forces came under attack from Lamia. Ruuvitar used his magic to seal himself, the egg, and several Argonian prisoners he could experiment on inside the ruin's inner sanctum, leaving all his soldiers to be killed by Lamia and the Pact forces converging on the ruins.
One Dominion soldier, a Khajiit named Kazdi, hated Ruuvitar even before he left her to die. When the Vestige entered the ruins, she aided them in unlocking the inner sanctum to get back at Ruuvitar. The Vestige and Vicecanon Heita-Meen then confronted the Dominion leader and slew him.