Judith Mossman

Dr. Judith Mossman is a scientist who plays an integral role in the Half-Life 2 series. She is a cunning and manipulative triple agent, aiding both sides during the Uprising but eventually siding with the Resistance. Later on she discovered a secret and powerful project that could be used against the Combine, in a vanished ship named the Borealis.

Before the Black Mesa Incident, Mossman was a promising, up-and-coming research scientist. She applied for the same post as Gordon Freeman at Black Mesa, but lost out to Freeman's Innsbruck experience (as said by Eli Vance in Black Mesa East) and Isaac Kleiner's personal recommendation.

History
Years after the Combine invasion, Mossman became an important member of the Resistance base Black Mesa East, where she partnered with Eli Vance in making scientific advances to aid the Resistance war effort. Unbeknownst even to Alyx Vance, who disliked her, she also spied for the Combine, and reported directly to Dr. Wallace Breen. How and when she took on this role is not known, but Breen's impatience with her and his remark that the Combine "could have taken Eli Vance at almost any time in the last several years" suggests that she acted as a double agent for some time before Freeman's reappearance. She also leaked the secret of uni-dimensional teleportation to the Combine, a technology they had previously lacked.

Personality
Mossman has a friendly if cunning personality, tempered by a certain amount of arrogance. She does not get on well with Alyx Vance, due to what Mossman considers is Alyx's blasé attitude towards the Resistance's scientific equipment, and also possibly due to Mossman's attraction to Alyx's father, Eli. According to Alyx, Mossman, despite her overtly courteous manner towards the protagonist, nurses resentment against Gordon Freeman due to his appointment over her at Black Mesa; she believes that "it should have been her in the test chamber that day". Despite her cynical manipulations of all of these characters, however, she is apparently able to reconcile her differences to defeat the Combine.