Mallon was a Gatherer that lived at the outpost on Gamma Hromi II.
In 2366, Mallon was left in charge of the Gatherers by Brull while Brull planned to be aboard the USS Enterprise-D to engage in peace talks with Sovereign Marouk, the Acamarian leader, and Gatherer leader Chorgan. (TNG: "The Vengeance Factor")
Mallon was played by J. Softley.
According to the Star Trek: The Next Generation Companion, 2nd ed., p. 109, Mallon was played by Marina Sirtis' husband Michael Lamper. He actually played another unnamed Gatherer.