Golo'Mekk vas Usela

Golo'Mekk vas Usela is an exiled quarian for selling his people to the Collectors, spy of Cerberus (Mass Effect) and main antagonist of novel Mass Effect: Ascention.

Story
A decade earlier Golo belonged to the Usela's crew, one day he made a deal with the Collectors. They wanted 24 'pure' quarians from the Flotilla, meaning never gone on their Pilgrimage. Golo sold his own people in exchange for new technology, but he was discovered and punished with a dishonorary exile. Golo established himself on Omega.

Golo managed to survive on Omega despite the harsh and dangerous conditions there. He eventually became a Cerberus contact. In 2183, the Illusive Man becomes more interested in the Migrant Fleet, and wants the Fleet's codes to monitor its movements and communications. Golo promises Pel he will help in getting the codes.

Golo contacts a scout ship from the Idenna, the Cyniad, and claims he has vital technology to sell. Feda'Gazu vas Idenna agrees, with caution, to meet Golo on the planet Shelba to make the exchange. Though she and her crew comes prepared for treachery, they aren't prepared for an ambush by Cerberus forces. Golo helps to capture Hilo'Jaa vas Idenna, the Cyniad's pilot, who becomes enraged when Golo uses his old quarian name and insults him by referring to him as "Golo vas Nedas" or "Golo nar Tasi" (meaning 'crew of nowhere'; 'child of no one'). In response to the insult, Golo spitefully smashes the faceplate of Hilo's environmental suit.

After doing his part, Golo returns to Omega, but Hilo contracts a virulent disease, making it harder for Pel to interrogate him and get the codes for the Migrant Fleet. Golo offers to make amends to Pel by extending an offer from the Collectors, who are interested in buying healthy human biotics — like Gillian Grayson. Once he has passed on the offer Golo believes he is safe, only to run into Lemm'Shal nar Tesleya.

The young Lemm has heard of the Cyniad ambush and suspects Golo's involvement. Under interrogation at gunpoint, Golo claims he was only the middleman, and, playing friends, sends Lemm to find Hilo, who is being held captive by Pel. Golo tips Pel and his men off beforehand, hoping Pel will kill the younger quarian, but Lemm, mistrusting Golo, launches a surprise attack before they are ready.

Lemm escapes to the Migrant Fleet with Kahlee Sanders, Hendel Mitra and Gillian Grayson after rescuing them from Pel's warehouse. Eager to recover Gillian, the Illusive Man contacts Golo to help get them aboard the Flotilla, using his knowledge of Fleet protocol. Golo is offered a high sum of credits, but is also happy to exact revenge on the people who had exiled him. He and Paul Grayson travels to the Fleet together in the stolen Cyniad, gets aboard the Idenna with Hilo's code phrases, and launches a surprise assault.

Armed by Cerberus, Golo kills many of the Idenna's crew in the attack, then catches Kahlee Sanders attempting to rescue Gillian. Golo beats Kahlee into submission as Paul Grayson stands by and watches. Grayson has a change of heart, choosing his daughter over Cerberus. He warns Golo to stop beating Kahlee, but then Paul, who never liked the quarian because he is willing to sell his own people for personal gain, shoots the quarian traitor in the head.