Commander Oneir Kadil was a mentally unstable salarian STG operative and Shadow Broker assassin who was often sent to participate in "insane" and "suicide" missions that few other people would undertake.
Born on the colony of Karroticum in 2169 CE, Oneir Kadil grew up a kind and caring person, with a love for the army. In 2179 CE, he joined the salarian STG, where he became lieutenant commander and developed a deep bond with all of his team. However, in 2183 CE, he lost his whole team to Saren's geth on Virmire. He went insane after seeing his team die, believing that he'd failed them. The STG discharged him and tried to offer him counseling, but he refused and killed two fellow salarian STG who attempted to forcibly commit him to a mental hospital.
He ran to Palaven, where the Shadow Broker hired him as an assassin. He accepted, still succumbing to his insanity. He worked for one year, mainly killing Blue Sun mercenaries in an effort to weaken their structure and hopefully stop their force deployment to the Terminus by making them reinforce their presence in Council Space. He found the work strangely therapeutic, and for a time, he was able to stop thinking about the deaths of his STG squadmates.
In 2184 CE, Oneir was assigned to assist fellow operative Vornel Demarian in the Green Day Massacre, a vicious strike on the funeral of rival information broker Farouk Amanesu. Oneir provided sniper fire, killing six police officers and one of the late information broker's top lieutenants. But he grew disturbed when his teammates started killing Amanesu's family, and decided to start targeting his teammates instead. One of his fellows, Julia Cerold, realized what he was up to and killed him.