Teresa: You two worked together, right?
Gabe: We were partners. My first year with the Agency.
Addison Hargrove is the former lover of Gabriel Logan, she is also the mother of Blake Hargrove, Gabriel's daughter.
Syphon Filter: Dark Mirror
Agent Hargrove once worked in cooperation with Gabriel Logan prior to the Syphon Filter incident and Lian Xing's defection. They developed a trust between them that became a relationship, both in professional and romantic terms.
In 1994, Addison left the Agency and gave birth to the child Gabe had fathered, a girl she named Blake. Hargrove wanted to harbour her daughter from the dangers of her career, and by 2006 she was working for the KemSynth corporation in Iquitos, Peru, assisting with plant harvesting for Project Dark Mirror.
Red Section attempted to secure the nerve gas for their purposes and kidnapped Blake to demand a trade for Dark Mirror's data. Gabe found about her association with KemSynth and helped observe the trade between her and the paramilitary operative Touchstone. Addison presumably died from falling off a mountain, but saved herself with a harness.
A memorial was left in her name at Arlington Cemetery, making her officially dead and allowing her to live safely with Blake because of Logan's rescue. Gabe Logan did not retire with them, and continued to work for the Agency.
Syphon Filter: Logan's Shadow
Addison appears in a picture with Blake, that is the one Gabe sees before departing in a mission. She is also mentioned by Cordell, that says that the only thing Gabe has is going back with his family and the private sector. At the end of the game he tells Lian that he is going back with his loved ones, but then Mujari is killed, and Teresa and Gabe are presumably mortally wounded by her who is killed by Gabe, and Lian tries to revive him and the game ends on a cliffhanger ending.
- Shoved off a platform and over a railing by Stuart Coleman (Touchstone) when she fails to bargain with the latter.
- Her death being staged is a clear reference to Teresa Lipan's coffin-hopping in SF2, before Lipan reveals she survived in SF3.