Ian Edgerton (Lou Diamond Phillips) is an FBI Agent, and probably the most memorable character on Numb3rs relative to his total of appearances (9). He is not part of the LA team led by Don Eppes but rather a maverick, a hunter who brings in the criminals no other agent can seem to track down. He first appears in "Sniper Zero", setting his real-world experience against Charlie's models. However, from the beginning he shows respect for Charlie and the other academics which is generally reciprocated, and seems (for him) genuinely upset in "Cause and Effect" that he didn't get an invitation to the lucky professor's wedding to Amita as the curtain comes down.
Among his unexpected aspects and many talents, Edgerton shows professional-level skill as a sketch artist in "Toxin".