Nikki Carpenter is an undercover CIA operative. She formerly worked as a hacker for DXS until she faked her own death in the Pilot Episode.
She and MacGyver (Lucas Till) were in a romantic relationship for about 2 years. It was Jack Dalton (George Eads) who had introduced them to each other before she joined MacGyver and Jack for DXS field missions.
In Episode 1×12, it’s revealed that Nikki was actually framed by Patricia Thornton (Sandrine Holt) for being a mole. Mac asks Nikki if she is going to come back to Phoenix, but she reminds him she still has to take down the terrorist group.
Reboot series (Season 1)1×01 The Rising
The pin for her smartphone is MacGyver’s birthday.