Berenyi

 was a Time Lord. She graduated from the Academy with a degree in bio-chronology, and left Gallifrey to become a Designer. As a mercenary hired by wealthy clients to alter time, her work on "an assassination in a theatre in 1865" had attracted the attention of an unknown German from the 22nd century, who hired her to go to 1963 and design the assassination of John F. Kennedy. She programmed a human male — who had been the chairman of the Fair Play For Cuba committee and who had a Russian wife — to shoot the president. As a part of her "design", she had established that Jack Ruby would kill the president's assassin.

A red-headed smoker at the time of the Kennedy assassination, was also given to wearing exclamation points, perhaps indicating she knew of the Doctor's affinity for wearing question marks. Like the Doctor, she possessed a fairly detailed knowledge of Earth culture and history. She seemed well-versed in the pop culture of the 1980s and was known to like The Jesus and Mary Chain, Sonic Youth, Cherry 7UP and Arthur Miller's biography.

She also had her own TARDIS. It presumably had a working chameleon circuit, since it was disguised as a filing cabinet in the book depository from which Kennedy's assassin operated. (BE: Untitled)

It is possible that she was working alongside The Master, who was also working on the assassination. (MA: Who Killed Kennedy)