Gial, or possibly "Ernie"
The first reference to his forename seems to have been in The Essential Guide to Warfare
Gial Ackbar was born into a prominent merchant clan in the city of
Foamwander, served his planet's king during the Clone Wars, and held
high military and political office m the early years of the Imperial
era. At first. Ackbar saw the New Order as restoring Republic law and
justice—but the Empire soon brought an invasion fleet to his
homeworld. The peaceful cultural and technological achievements of Dac
had to be suppressed to preserve the idea of human superiority.
This name was then canonised in the index of Star Wars: Absolutely Everything You Need to Know.
Admiral Gial Ackbar - P171
Interestingly, in the excellent Making of Star Wars: Return of the Jedi we learn that Lucas and the crew would refer to the Ackbar puppet on the dailies as Ernie Ackbar.
Main unit next moved to Stage 5 and the rebel briefing room, which
meant first days for Blakiston, Crowley, and Tim Rose (Ackbar, or,
sometimes, “Ernie” Ackbar, on the Progress Reports). In wide shots,
Ackbar was a man in a suit; in closeup, a puppeteer would manipulate
his facial movements from below. Although still “immersed” in
Poltergeist, Richard Edlund arrived to oversee the VistaVision shots
on that set because, in postproduction, a hologram of the Death Star
was to be added by the Computer Division.