Rat worked with and on the Crepitus alongside Gabby and holds a significant amount of information on the creatures. The man will appear in Cambria after Gabby mentions his name when you talk to him.
A man of nervous and suspicious disposition (not to mention a suspicious nickname), Rat won't give up his information easily, and usually needs to be threatened in conversation before he will tell you anything useful.
While he wasn't a scientist, he did act as a caretaker and handler of the terrible creatures in their lair below the mines of Arulco.
Sector G9, Cambria Commercial