During the First Contact War, Ahern was given a near-suicidal mission to retrieve a data module, with only a small squad, against dozens of turian mercenaries. The mission was a success, but Ahern's experiences in the war left him prejudiced against turians. However, Ahern did not succumb to racial hatred; rather, he gained a candid appreciation of the advantages, and limitations, of turian military doctrine.
After the war, Ahern eventually worked up the ranks to admiral, and was given command of Pinnacle Station — once a turian command center during the Krogan Rebellions, though now a training facility run by the Citadel Council. Ahern claims he was a good choice for the position, because someone who knew how both humans and turians fight was needed. Ahern set about making Pinnacle Station into a first-class training facility for elite competitors, hoping to teach a few turians to think outside the box — though he claims the endeavour is about as easy as "teaching a krogan to be pretty".
Ahern will comment on Shepard's progress during the simulated missions, offering either encouragement or derision depending on the Commander's performance.
Ahern tends to be a very sarcastic and hard to please individual. Even after Shepard successfully sets new records in the simulators, he often has back-handed compliments for the Commander, such as complimenting Shepard's "ability to weigh the pros and cons of standing in the way of incoming fire", or saying that Shepard can add "a broken record to the list of things you've ruined".
When Shepard arrives on Pinnacle Station, and has completed every tier of combat scenario, Admiral Ahern tells Shepard there is only one special scenario left: a recreation of the module-recovery mission the admiral fought in during the First Contact War. Shepard tells Ahern to turn off the safeties, and takes on the challenge as a wager: Ahern offers his retirement home on Intai'sei, while the Commander accepts that this may be a fight to the death. Ahern is reluctant to let Shepard try, not wanting the first human Spectre to die in his simulation. After fighting a hard battle against waves of turian mercenaries, Shepard emerges victorious, and Ahern honors his agreement, giving Shepard access to the apartment. In parting, he tells Shepard "Call me Ahern, you've earned that too."
In the apartment, a personal computer with a message meant for Ahern allows Shepard to order random, but sometimes extremely rare, weapons, armor or upgrades from three different price tiers from a local trade convoy. It is possible for Shepard to return to Ahern and mention that they are getting his deliveries, to which he responds that if Shepard can pay for them Shepard can keep them.