Batiste was a reconnaissance agent sent through an inter-dimensional rift to spy on the United Federation of Planets. Provided with an isomorphic compound, to hold off the effects of the reversion for several years, Batiste was able to infiltrate Starfleet Command, attaining the rank of admiral. He is described as a robust man in his mid-50s.
At some point, Batiste married Afsarah Eden, however their marriage was a difficult one from the start - when Batiste insisted on working on the first day of their honeymoon, rather than visiting Delgara's botanical gardens. The couple divorced in 2376.
Following the return of the USS Voyager from the Delta Quadrant, in 2377, Batiste manoeuvred himself in to the command structure of Project Full Circle. Realising the futility of his mission, but unable to accept suicide (as per his orders) as a valid alternative, Batiste began to formulate a plan by which he could return home. Over the next three years he would petition several times for Starfleet to return to the Delta Quadrant, but each time his proposals would be rejected by Starfleet Command following objection from Voyager's former captain, Kathryn Janeway.
Following Janeway's death in 2380 and the events of 2381, Starfleet finally commissioned a task force to return to the Delta Quadrant, charged with exploration, and establishing, if possible, whether the Caeliar remained in this galaxy. Batiste ensured he was assigned as fleet commander for the expedition. He also overruled counselor Hugh Cambridge's psychological assessment of Captain Chakotay and assigned his ex-wife Captain Eden as commander of the fleet's flagship, Voyager.
Shortly into the mission, Batiste began sabotaging Voyager as a distraction from his activities. He also took advantage of the fleet's rendezvous with Chakotay and Seven of Nine, casting suspicion for the sabotage upon them. When an initiative by B'Elanna Torres, who had also rendezvoused with the fleet, threatened the success of his plan, he used his authority to have her restricted from engineering. Around this time, he was also coerced into cooperating with the Indign consciousness which had inhabited the 'body' of the advanced Emergency Medical Hologram, Meegan McDonnell.
Finally he succeeded in maneuvering Voyager to an appropriate location to open a rift to fluidic space. However, before he could escape, he was discovered and confronted by Captain Eden. Batiste confessed everything to Eden, including the revelation that their marriage had been part of the operation and, although he had tried to, he had never loved her. Although clearly deeply hurt by his betrayal, Eden allowed him to take a shuttlecraft and leave.
His journey almost over, he neutralized the isomorphic compound in his body, allowing him to return to his natural form. He was, however betrayed by 'McDonnell' who opened the shuttle's hatch, flushing him out in to space. He was rescued by the species 8472 member known as Valerie Archer, who had emerged from the rift created by Batiste. Although initially refusing to accept him, due to his potential as a 'pollutant' to the fluidic space, Eden and Chakotay were able to convince her to finally allow him to complete his journey home. (VOY novel: Full Circle, VOY novel: Unworthy)
- • Note: Whether 'Willem Batiste' was a persona created specifically for purpose, or whether a human by that name was replaced by the agent is not clear.