Lincoln Cain is an agent with the AST.
The acronym here stands for Australian Security Taskforce, "a relatively secret organisation dedicated to protecting Australia's security both at home and overseas", referring to itself as "the frontline defense when it came to espionage and terrorist threats". It is interesting that the earlier description used the word 'relatively' because we are told elsewhere that the AST goes to impressive lengths to keep itself unknown to just about everyone. "Now the Australian Security Taskforce don't just have an unlisted number, they have a set of procedures you go through before they make any contact with a member. So Lincoln found a quiet corner and began dialing on his newly acquired phone. The phone rang a few times, then the familiar beeps of an overseas call came through. "Darlinghurst Drycleaners." There were specific code phrases used in the call which if not delivered quickly and correctly would leave the operative out in the cold.
Cain comes to the AST via the military. He "was a veteran of three campaigns in Afghanistan, even though he was in his late thirties. He stood 188cm (6'2") with short wavy blond hair with a muscular physique hardened from years of training and combat. His dark piercing eyes and broad chin disguised his rather affable nature. He looked like your typical rugby player with those broad shoulders. A decorated army colonel, with his tour of duty over, his civilian life was never going to work. He knew it, the Australian Government knew it and his immediate bosses knew it. That's when the Australian Security Taskforce took over".
As we follow his time with the AST and he moves into his forties, he continues to keep his physical shape in peak condition and he takes pride in the fact that not only was he a "successful field agent, but a trainer for other recruits and before long, quite a legend within the organisation". Despite his successes, though, he was "totally unknown outside of the Team, even other organisations like the CIA and MI6 had never heard of him. But that's the way he liked it. He could move freely around the world without drawing attention".
For all his skills and experience, which are extensive, he is human as we learn in the very first recorded adventure when "despite his years of training and experience in the art of covert surveillance, agent Lincoln Cain of the AST found himself in a warehouse surrounded by heavily armed enemy guards". He is chastising himself for his rookie mistake and fairly certain he would pay the ultimate price for his screw-up but he does take some macabre pleasure in that "no one was aware that he was there" so while no one would be coming to the rescue, no one would know about the oops..
One other factor that proves Cain is human is that Cain admits that he does have a fear of heights which he has to deal with and does so with difficulty, and with the help of Maddy.
Maddy is a woman who, several missions into our following Cain, partnered temporarily with him. Madeline Jackson, a woman described to him initially as being "a little unconventional, and not your typical explosives expert", moderating that a tad with "then again, I don't think there is such a person as a typical bomb jockey." When he actually meets this woman, someone who will become very important to him, she somewhat jokingly cautions, "I am a bomb technician. If you see me running, please try and keep up". Maddy will prove to be a whole lot more than that, as impressive as that alone is.