GUARD, also known as Lexa, is a Loric character who ran a conspiracy theory blog and met Mark James on it. Mark told her everything he knew about the Loric and the Mogadorians. Lexa helped Mark try to make the public aware of the Mogadorians and evade them himself.
Lexa is described as about a head taller than Mark. She has dark skin and short hair in a Mohawk. Mark estimates that she is in her mid-thirties, but admits that he could very easily be incorrect. Mark also states that she would look equally comfortable on a magazine cover and a battlefield. The first time Mark sees her, she is wearing a motorcycle helmet and leather jacket and the second time, overalls.
She is quite secretive on the Internet, and, when she first calls Mark, she uses a disguised voice. She seems to be quite rich, as she can send Mark gadgets, cash, a truck, and owned two safe houses. She presumably knows how to shoot a gun well, and is very good with computers.
In Return To Paradise, Mark James sees a theory online on a blog called "Aliens Anonymous" that the disaster at Paradise High School was alien related. Mark confirms it to GUARD. GUARD and Mark talk on the blog chat frequently about interesting news and Mark's own life. GUARD eventually helps Mark steal Purdy's laptop.
In The Fugitive, Lexa meets Mark at a gas station. Mark assumes that GUARD didn't come personally, but sent someone instead. GUARD and Mark are communicating throughout the book, and GUARD sends Mark cash, gadgets, maps, and a truck. GUARD also lets Mark into a safe house, but was constantly tracking him. She ends up blowing up the safe house. Eventually, when Mark and Sarah enter another of her safehouses, she points a gun at them, but eventually lets them in. She then tells them that her name on Lorien was Lexa. By the description of The Navigator, she is revealed to be a Cêpan.