O'Halloran

From Memory Alpha, the free Star Trek reference

For the member of Species 8472 who impersonated this individual, see O'Halloran (Species 8472).

Ensign O'Halloran was a Human Starfleet science division officer during the 2370s.

In 2375, O'Halloran's identity was unknowingly assumed by a member of Species 8472 as this species prepared to infiltrate Starfleet, and possibly invade Earth. (VOY: "In the Flesh")