David Gentry, serial number 99B3278, was the identity assumed by a member of Species 8472 in 2375 when that species constructed a re-creation of the Starfleet Command complex in preparation for an infiltration and possible invasion of the Earth.

The replicant accosted Chakotay and Tuvok on the grounds of the re-created complex, telling them as they had entered a restricted area. Chakotay and Tuvok were there investigating the re-creation. He was incapacitated by Tuvok using a Vulcan nerve pinch and taken aboard the USS Voyager.

Aboard Voyager, Gentry had at first thought he was experiencing a simulation to test him, but soon realized it was quite real and he had been captured. When The Doctor, Voyager's holographic chief medical officer, attempted to take a genetic sample from him to uncover the identity of his species, he committed suicide by releasing a cellular toxin into his own bloodstream. Later, The Doctor succeeded in uncovering his species' identity by using a cytokinetic injection to trigger a reversion to his corpse's true form. (VOY: "In the Flesh")

Gentry was played by actor Zach Galligan.
It is unclear if there was a real David Gentry in Starfleet, or if the person was created by Species 8472.
The Star Trek Encyclopedia (4th ed., vol. 1, p. 301) described the persona created by Species 8472 as a re-creation of David Gentry.