Gavin is the tertiary protagonist in the Slender / ARG Series, 5zer02.
Gavin, Tyler, and Xakk originally started the 5zer02 web series to film the city and area around Louisville, Kentucky. Eventually, the audio and video is seen as distorted and the three begin to grow more paranoid, notably Xakk. During the time Xakk goes missing and their being hunted by the Slender Man, Gavin suggests that he and Tyler stop filming. A possessed Xakk then uploads videos warning them to keep filming, to which they decide to.
Upon Xakk's return, Gavin didn't take too strongly to the idea of accepting him after the times he had attacked them, but Tyler convinces him to do so. During his brother, Josh's, visit, Gavin tells Tyler and Xakk that their grandmother had murdered their grandfather. Josh is then killed and taken by the Slender Man.
Gavin isn't seen as much in Season 2, as he has fallen into an isolated depression. At one point, Xakk mentions that Gavin had kicked him out of his house blaming everything on him. Eventually, Tyler and Xakk help him out of his depression by taking him to his favorite restaurant on his birthday. After Xakk's girlfriend, Kayle, goes missing, Xakk sets off on his own adventure. Gavin and Tyler aren't seen or heard from again.
Whether or not Gavin knows about the video that shows his brother revived is unknown.
Its likely Gavin will appear in Season 3, along with Tyler and possibly Xakk.