Alex Kralie was a film student and friend of Jay. He was the writer, director, and producer of his 2006 drama Marble Hornets, but when he began encountering a figure known as the Operator, he began acting strangely—drawing things, writing foreboding words, acting unusually aggressive, and obsessively keeping a video camera on himself at all times. Eventually he canceled the project entirely and attempted to destroy all of the tapes he had recorded. Instead, Jay convinced him to hand over the tapes. Alex told Jay to burn them. Jay did not.
After that, Jay did not see Alex again, as Alex moved and changed schools. Jay did not hear from Alex for three years.
Then, on April 4th, 2010, Alex's girlfriend found an old video camera of his. It turned out that he was still alive and thriving, elsewhere, with a girlfriend and a new house. He was seen working on something on his laptop until his girlfriend came into the room with his old camera, still filming (over old tapes, no less). She knew nothing of his past as a film student, and as soon as he saw the camera, he reacted strongly—a reaction that was justified as the Operator appeared no less than moments later, approaching them from the hallway. Alex guided his girlfriend out of the house, presumably to safety.
Alex at least survived the encounter, as he is seen later in the series chronology. He met up with Jay again in Entry #35, where he is seen apparently aware of Tim's presence in the dilapidated house that was the return address on the tape sent to Jay in Entry #26. He holds down Tim while Jay unmasks him, and then apparently attacks Tim with a large rock.
(Editor's Note: Fill in information from season 2.)
In Entry #64, Alex is heard calling Jay to tell him and Tim to leave the tunnel in Rosswood Park. In Entry #67, Alex is seen in the Hospital and is assaulted by the Hooded Man and Tim directly following the events of Entry #65.
Alex's middle name does not start with R. His initials are confirmed to not be A.R.K.
If Alex was only 5 or 6 in in enttry 37, he wouldn't yet be living near Rosswood or the other park, as the original Something Awful thread says that Alex was 8 when he moved to that area. The Operator is not tied just to those parks then, he was following Alex before Alex was connected to them. ~ Kaylee2014
Based on enttry 37, it can probably be assumed that his birthday is April 4th. His birth year is probably 1982, 1983, or 1984. ~ Zeta Kai
According to the number of candles on the cake in the video, Alex would have been five or six years old at the time, making his birth year 1985 or 1986. ~ Zarggg
Based on the entries leading up to Entry 52, particularly the entries where The Operator is seen in Alex's house (but Alex does not run away) and the entry where Alex kills the man in the tunnel (and The Operator disposes of the body), I strongly believe that Alex is working with the Operator, likely to lead Jay into a trap. ~MrAnon515
Maybe his surname is a pun: "Kralie", splitted into two words remains in "Lie" and "Kra". If we mirror "Kra" it puts to "Ark", resembling to totheark. ~ Stickend