Alan Kistler was a protection agent for Federation President Nanietta Bacco, serving in that capacity since the beginning of her term. He was of mixed Peruvian and Irish ancestry, which gave him fair skin and dark, wiry hair.
During the Borg Invasion of the year 2381, President Bacco attempted to rally a fleet made up of ships from a number of local interstellar powers to fight the invading Borg Collective and held a summit with numerous ambassadors. Kistler and several other protection agents were present as security when Tholian Ambassador Tezrene confronted Bacco, and flanked the enraged political figure when she stormed out. (ST - Destiny novel: Mere Mortals)
When the Borg reached the Sol system, Bacco and select members of her cabinet gathered in the Monet Room, where they expected to witness their destruction, protected by Kistler and fellow protection agent Steven Wexler. However, thanks to a plan enacted by several Starfleet vessels - the USS Enterprise-E, USS Aventine and USS Titan - and a race known as the Caeliar, the invasion was halted and the Collective destroyed forever. Due to this, former Borg drone Seven of Nine collapsed in the Monet Room. Kistler called for a doctor and then saw the doctor and a pair of medical technicians inside. In the aftermath, President Bacco addressed the Federation, with Palais de la Concorde Press Liaison Kant Jorel and Presidential Chief of Staff Esperanza Piñiero by her side. Kistler and Wexler escorted them to the stage and then off and back to the President's office. (ST - Destiny novel: Lost Souls)
In 2384, Kistler was killed along with Wexler in the "safe room" of the Bank of Orion while protecting President Bacco and Imperator Sozzerozs of the Gorn Hegemony from Breen android assassins. (TNG - Cold Equations novel: Silent Weapons)