In 2364, Aaron held an important position at Starfleet Headquarters. At some point, Aaron became infected with a parasitic being and was under the control of an alien mother creature that had taken residence in Lieutenant Commander Dexter Remmick.
When the USS Enterprise-D returned to Earth to respond to suspicions of a conspiracy orchestrated by these creatures, Aaron greeted Captain Jean-Luc Picard and invited him to dinner. When Picard arrived, co-conspirators Savar and Tryla Scott, as well as several security commanding officers, all joined Aaron in cornering him in a dining hall and showing him how their people fed on live vermicular lifeforms.
When William T. Riker posed as one of the possessed officers in order to recover Picard, Aaron fired on the Enterprise officers and fled, seeking Remmick. Picard and Riker disabled Aaron with phaser fire just outside of Remmick's communications room. The parasite fled Aaron's fallen body and was ingested by Remmick. (TNG: "Conspiracy")
Admiral Aaron was played by Ray Reinhardt.
This senior admiral was originally named "Richard Erik". He was called that in a story outline which Tracy Tormé sent as a memo to Maurice Hurley on 3 February 1988 (while the episode had the working title "Assassins").
Aaron was described in the script as "old and lean – hollow cheeks and cold, piercing eyes, beneath a shock of white hair." 
Aaron's rank insignia, a triangle with two pips, would seem to place him above Savar and Mark Jameson, though all three are only described as "admiral". Savar and Aaron are described as "senior admirals" in the script. 
In the game Star Trek Conquest, Aaron was a player character in a reality where the Milky Way Galaxy was embroiled in conflicts between multiple species and cultures. In 2364, Aaron held the rank of commodore and was in command of a fleet during the conflict.