Johnson (Children of Earth: Day One)

Agent Johnson was a trained government official tasked with infiltrating Torchwood three to assess how well equipped they were. Her primary motivation is to "protect the state", even if it requires her to commit cold-blooded murder.

History
She placed Rupesh Patinjali in the field to masquerade as a potential new member for Torchwood. However, after months of perfect infiltration, the plan was abandoned when, following the reappearance of the 456, she received orders from John Frobisher to terminate Captain Jack Harkness. Under Johnson's orders, Patinjali lured in Harkness and shot him. After confirming that Harkness did indeed recover from the seemingly fatal wound, Johnson had a bomb surgically placed in his abdomen, in an effort to destroy the Hub and sever Harkness's theoretical connection to the Rift, in hopes it was the key to his immortality. Deciding that Patinjali now curtails a security risk, having blown his cover, she cold-bloodedly shoots the man in the back and has his corpse placed next to Harkness. (TW: Day One)

Johnson positioned a team at Cardiff Bay to eliminate any survivors of the Torchwood team, but they failed to catch Gwen Cooper and Ianto Jones, who made their separate escapes. She and her men coerced PC Andy Davidson into leading them to Gwen's home, where she again eluded capture, shooting the tires of Johnson's vehicle. The next morning Johnson supervised the search for Jack's body and when remains were found she ordered them transported and sealed within a remote military compound. When Jack's body eventually reassembled and regenerated, Johnson opted to have him encased in cement to keep him contained. However, Gwen, Rhys,and Ianto infiltrated the base and smashed Jack out of the cell with a fork-lift truck. Johnson and her men pursued the group, but were cut off in their pursuit by an exploding lorry Gwen and Rhys placed in the middle of the road. She then phoned Mr Frobisher and apologised for their failure. (TW: Day Two)

The next day Johnson's team located Alice Carter by tracing her phone call to the authorities inquiring after Jack. Investigating her mysterious background, Johnson's team eventually determined that Alice was Jack's daughter. Johnson led the team that stormed Alice's home and eventually cornered her in alley outside as she made her escape with her son, Steven. (TW: Day Three)

Johnson grew agitated as she found herself kept increasingly out-of-the-loop. Nonetheless, Johnson continued to pursue the Torchwood team. She led the strike force that confronted Gwen at the abandoned Torchwood 1 holding facility that the team had been using as their temporary base. However, she was forced to stand down when Gwen revealed that Torchwood had blackmailed Johnson's superiors in the government. (TW:Day Four)

After her encounter with Gwen Cooper and realisation of what the government was doing, Johnson had a change of heart and helped Torchwood's efforts. She released Alice and protected her son (occupying his time by having some of her team play football wth him), and later broke Jack out of prison. She provided him with the equipment needed - as well as getting Dekker - to analyze the 456's signature wave frequency. Using these assets Jack finally managed to defeat the 456, sacrificing his own grandson. (TW: Day Five)

Personality
Much as James Bond was considered a "blunt instrument" for Her Majesty's Government, Johnson (whose first name is unknown, assuming Johnson is actually her real name) follows the principle of "the end justifies the means". During The 456 crisis, she commits murder on at least one occasion (and is complicit in at least one other killing, namely the killing of a patient by Patinjali in order to lure Harkness).

Johnson initially exhibits a suitably cold-blooded personality, although she appears to enter into a respectful relationship with Harkness' daughter, Alice Carter, to the point where she agrees to keep from Alice's son the secret that Jack is his grandfather, not his uncle.

Despite this, and her willingness to change sides and help Torchwood, Johnson doesn't show any real emotion until she witnesses Steven Carter's sacrifice.

Behind the scenes

 * Aspects of Johnson's character can be traced back to the character of Space Agent Sara Kingdom, who like Johnson is initially depicted as cold-blooded and ruthless but changes her attitude over time.