Rosarev was a former Andorian Starfleet captain who rose to become the President of the United Federation of Planets. (The Dominion War Sourcebook: The Fires of Armageddon, Dominion War Timeline)
Rosarev was known for his support of a more aggressive defense policy to defend the Federation during the lead up to the Dominion War. After the resignation of Jaresh-Inyo in 2373, he was elected by the Federation Council to be the next President.
During the Breen Attack on Earth the Breen destroyed Empyrean House in Paris in an attempt to kill Rosarev but he escaped.