Lizzy Gill worked for Zeus Genetics and appeared only in the Season 8 episode 'Essence'. She was introduced at the beginning of the episode by Margaret Scully, who insisted her daughter needed someone to help out during her pregnancy.
Lizzy was later discovered to be a scientist working for a faction interested in Scully's baby, and the supposed superiority of its genome, when she was found replacing Scully's prenatal medication with a substitute. The substitute was later declared to be harmless by Scully's doctor. Lizzy Gill was one of the first and only to offer any type of proof that Scully's baby, while a miracle, was not (directly) the product of interference by anyone. When being interviewed by Mulder, Doggett and Skinner, Lizzy states that 'one could only hope to create that in a lab'. This statement is one of the stronger pieces of the evidence that supports the theory that Mulder is (William Scully) Jackson Van De Kamp's biological father, as he is the only person who is known to have been involved with Scully at the time.