Ackbar is a member of the Mon Calamari species from the planet of the same name. The Mon Calamaris are amphibious shore-dwellers, that prefer to be on land, but can stay in water for long periods of time. Ackbar is a male and is about 1.8 meters tall.
Before the Alliance
After the Empire emerged, it started to seize property on the planet Mon Calamari. The Mon Calamaris decided to passively protest. This was not tolerate by the Empire and they destroyed three of Mon Calamari's floating cities and enslaved many of the inhabitants. Ackbar was amongst those and was sent as a gift to Grand Moff Tarkin.
It was by observing Grand Moff Tarkin that Ackbar learned about the Empire and their military operations. His knowledge would late make him very valuable to the Rebel Alliance.
The first contact Ackbar had with the rebels came when they tried to assassinate Grand Moff Tarkin. They failed, but they managed to free Ackbar from slavery. Ackbar decided to returned to the Mon Calamaris and lead his people against the Empire. He lead them through many conflicts, before deciding that they should join the Rebel Alliance.
In the Alliance
Ackbars most notable achievements during the war with the Empire is convincing the Verpine to join the Alliance, which would supply the Rebels with B-wing starfighters, and creating the Rebels attack plan for the Battle of Endor
. It was the first achievement that gave him the title of Admiral.
Ackbar commands the Mon Calamari Star Cruiser "Home One"