Ford Pines

The author is the mysterious and unknown writer of Journal 1, 2 and 3, spending the latter of their life documenting the secrets and mysteries of Gravity Falls with the aid of Old Man McGucket. The mystery of their disappearance and unrevealed identity has become Dipper's ultimate goal to unravel.

History
Over thirty years before the arrival of Dipper and Mabel, the author dedicated his life to discovering and documenting the paranormal secrets of Gravity Falls, recording his findings in a collection of journals. The crown jewel of his discoveries was the Universe portal, schematics for a portal capable of unlocking infinite new worlds. After six years of discovery, the author began to write his third journal, now beginning to fear he was being watched by those who would seek to use the data he collected for malicious intent. To ensure their protection, the author crafted a large, underground bunker designed to house a large laboratory for his various experiments, keeping it well-hidden within the Gravity Falls forest.

As the author continued their expedition, he soon befriended the dream demon Bill Cipher, believing him to be a genuine and classy creature. However, he quickly learned of Bill's trickery and realized his true form as a malicious and evil being, warning any who read the author's journals to never summon him back into the world. Now even more paranoid, the author resorted to continuing his writings through invisible ink, eventually decreeing that no one could be considered trustworthy within the town. The author then sealed the Bunker and hid the journals in various locations within Gravity Falls, attempting to separate the knowledge of the Universe portal and prevent it from falling into the wrong hands. The author's fate it left unkown, though it is said he hasn't been himself ever since.

In "Tourist Trapped," Dipper Pines discovers Journal 3 in its obscure hiding spot in the forest, and becomes infatuated with learning the true identity of the author.

Gideon refers to the author as a "brilliant and unknown" individual in "Gideon Rises," where a flashback shows the robed and hooded author burying Journal 2 deep in the forest.

The author is mentioned again by Dipper and Soos in the short "Mailbox," in which they both resort to asking the all-knowing Mailbox their true identity. The unveiling is never to be, unfortunately, as Mabel provokes it into self-implosion.

Dipper again questions the author's identity in "Scary-oke," eventually dedicating the rest of his summer to uncovering the mystery behind the author.

In "Into the Bunker," Dipper, Mabel, Soos and Wendy locate the author's abandoned Bunker in the forest. They eventually come face to face with one of their own experiments, the Shape Shifter, disguised as the "author". However, this guise turns out to be based off the mascot of a can of Baron Num Nums High Flyin' Beans, thus not revealing the true author's face. The creature attempts to steal Journal 3 to learn various new forms to take, ultimately being sealed in a cryogenic tube designed by the true author. Before freezing, the Shape Shifter warns Dipper that his search for the author's identity will lead him to a fate worse than death.

Soos inadvertently collects the author's laptop from the adventure, leading Dipper on a hunt to learn the eight-letter password protecting it in "Sock Opera." Dipper's quest is cut short when Bill Cipher commandeers his body and destroys the laptop, hoping to throw him off the trail of finding major answers in the town.

The author is heavily mentioned in "Society of the Blind Eye," in which Dipper continues his hunt to learn the person's identity and begins highlighting suspicious townfolk. His quest leads the gang, alongside Old Man McGucket, to discover a sinister secret society hidden in the town.

Appearance
Little is known about the exact appearance of the author due to their identity remaining unrevealed, however from the little that has been shown they appear as a tall figure wearing a black hood and robe as well as gloves to conceal any trace of skin. According to the Shape Shifter, the author has an extra finger on at least one of their hands, matching the covers of the three journals.

Trivia

 * The term for having more than five digits on one's hand is called 'polydactyly'. If the extra digit is after the pinky finger, such as seen on the cover of the journals, it is known as 'postaxial polydactyly'.