Nikki Betancourt

Nikki Betancourt joins the Violent Crimes Unit shortly before season five's High Exposure and proceeds to quickly clash with most of the team. However over the course of the show she warms up to them and she becomes a proper member of the team.

Backstory
Nikki spent four years in the Los Angeles Police Department (LAPD) before presumably attending Quantico to become an FBI Agent. She was then assigned to the Violent Crimes Unit in LA led by Don Eppes, where she replaced Megan Reeves on the team.

Personality
She is a confident and assured woman who knows what she wants, and has very strong opinions about right and wrong,

Numb3rs Season 5
Nikki joins the team in "High Exposure", though she resents being seen as a newbie, having spent the previous four years in the LAPD. She is originally a little prickly about the FBI's high-tech approach, and not remotely interested in Charlie's math and analogies, but she warms to him, and the team.

Nikki has express political ambitions, with no intention of sitting behind an FBI desk indefinitely, although in "Cause and Effect" it does seem as though she plans to stay with the FBI remainder of the team for the time being at least. She is a dedicated, clever and loyal agent who soon overcomes the chip on her shoulder. David, in particular, seems to frequently rely on her instincts and judgement.

Ian Edgerton
Nikki went on at least one date with Ian Edgerton after they met in High Exposure.