Born in Moscow, Russia (Soviet Union) as Masha Rostova, Elizabeth Keen, at the age of 4, was involved in a traumatic incident in which she shot and killed her father, the real Raymond Reddington, to stop him from attacking her mother, Katarina Rostova, then she moved to Nebraska and was raised by Sam Milhoan.

She had been with the FBI for 6 years and was head of the mobile emergency psych unit in New York. In “Pilot”, she was asked to profile herself by Harold Cooper and revealed that her subordinates in New York called her “sir” and thought her to be a “♥♥♥♥♥”. She is also revealed to have a degree in forensic psychology and graduated from Quantico a month before the series begins. Raymond Reddington reveals that she had highlights before the start of the series, and may have resided temporarily in Baltimore.

At about the same time she joined the FBI, she met Tom Keen and later married him, taking his surname.

It is later revealed in “Sutton Ross” that the real Raymond Reddington is her father, not the imposter who took his place 30 years ago and is currently known as Red. In “Rassvet”, Liz learns from her grandfather, who was located with Donald Ressler's help, that the man she shot the night of the fire was in fact the real Raymond Reddington while her mother's lover Ilya Koslov took on Reddington's identity to protect Katarina. However, Katarina's fate continues to remain unknown as Liz's grandfather has not heard from her in 28 years.

Liz was engaged to Nik Korpal. She was married to Tom Keen. She was in a romantic relationship with Donald Ressler.