President Adar was the last president of the twelve colonies before the Cylon attack and terminated by the Cylons, along with the first 42 members of his cabinet. He was on his second term as president, and had served as a mayor before that (Mini-Series).
Prior to the final Cylon attack against the Colonies, Adar had faced some political strife for military actions, which he himself apparently regretted. His regret manifested itself to the point of writing down the names of all the casualties of the act, leaving it in his desk as a reminder of his fallibility (Water).
Another of his actions in office was to offer a full pardon to Tom Zarek in exchange for the latter's renunciation of violence; Zarek turned down the offer (Bastille Day).
He was also an influential friend to Gaius Baltar. (Mini-Series)
Commander Adama considered President Adar to be "a moron" (Home, Part II).