Aventus lost his mother when he was about 10 years old; the fate of his father is unknown. Since he had no one else to care for him, Jarl Ulfric Stormcloak sent him to Riften to live at the Honorhall Orphanage. At the orphanage, he developed a strong hatred for Grelod the Kind, the headmistress, who, despite her name, was extremely cruel to him and the other children. Aventus escaped from the orphanage and returned to the now-deserted house in the middle of Windhelm where he lived with his mother when she was alive. When the Dragonborn encounters him, he is attempting to contact the Dark Brotherhood by performing the Black Sacrament.
In the absence of a Listener, the Dark Brotherhood hears about the Black Sacrament through local rumors. Rumors that Aventus is performing the Black Sacrament have spread across much of Skyrim. Hearing of the deed from an innkeeper, the Dragonborn may choose to answer the call. Confusing them with a Dark Brotherhood member, Aventus sends the Dragonborn to kill Grelod the Kind; it is impossible to dissuade him. If the Dragonborn chooses to do so, Aventus rewards them with a family heirloom.
With Hearthfire, it is not possible for the Dragonborn to adopt him, even if all requirements for adopting a child have been met.
- "When I grow up, I'm gonna be an Assassin, that way I can help lots of children, Just like you!"
- "Really, I mean, I knew the Dark Brotherhood was good... just not that good! You killed the old hag before I even asked!" (if Grelod is killed before talking to him)
- "I'll go back to the Orphanage in a while. I'll give them time to, you know... clean up the mess."
- "Sweet mother, sweet mother, send your child unto me for the sins of the unworthy must be baptized in blood and fear." (repeatedly, until the Dragonborn interacts with him)
- "I'm so tired..." (between bouts of praying and stabbing)
- "You came to visit! So much better now that Grelod's gone, thanks to you!" (This one only appears if another Aretino spawns in the orphanage)
- "No! It's not supposed to work like that!" (If the Dragonborn attacks him before talking to him.)