Mass Effect Edit
With the help of Jenna, Chellick is hoping to combat illegal arms trading on the Citadel. When Commander Shepard tries to talk to Jenna about the dangers of being a C-Sec informant, Chellick — in the guise of a drunk — bumps into Shepard on the way out of Chora's Den, whispering for Shepard to come to C-Sec before staggering off. He later expresses his annoyance that Shepard almost blew Jenna's cover, and asks for help in the investigation. In order to locate the dealers, he has a contact, Jax, from whom he needs to obtain illegal weapons modifications.
Shepard can pose as a buyer for the modifications down in the Markets, and either play the part carefully, leaving Chellick's contacts intact or go against Chellick's request and attempt to make an arrest. If Shepard ends up shooting Jax, Chellick loses all his leads and dismisses Shepard if the Commander tries to speak to him again. If Shepard maintains the cover, Chellick is very pleased with the outcome, and permits Jenna to quit her position as an informant and passes some of the modifications to Shepard.
- In Mass Effect 2, an Emily Wong news vid on the Citadel regarding Shepard's actions during Garrus' loyalty mission will refer to him as Executor Chellick, implying that he may have succeeded Executor Pallin as head of C-Sec. However, as Pallin remains Executor in Mass Effect: Retribution, which is set after the events of Mass Effect 2, this is likely a remnant of content ultimately cut from the game which revealed that Pallin was killed by geth during the Battle of the Citadel and that Garrus considers Chellick the 'safe' choice to lead C-Sec, but not the one he'd make.  Since Pallin canonically survived the events of Mass Effect, Chellick's position as Executor in Mass Effect 2 is likely a mistake. In this version of events, according to the C-Sec officer running a security check, Chellick allows Shepard to remain armed on the Citadel as the Commander tends to find trouble and "needs to be armed".