The Traveler

The Traveler is a trickster deity worshipped by Jester. As an NPC, the Traveler is portrayed by Matthew Mercer.

He seems to find enjoyment in mischief and pranks. When Jester rearranged all the books in a bookstore, she felt a sense of approval from her deity. He teaches Jester to steal and create chaos but always maintain the balance by giving something back.

Jester keeps a sketchbook that she appears to use as a means of communicating her experiences to the Traveler, and as a way of worship.

Jester's holy symbol for the Traveler is a door arch and path.

Appearance
When the Traveler appeared to Jester in her room at the Pillow Trove in Zadash, he was hooded in a cloak of deep green. She saw verdant irises in the dark space of his hood.

Jester confided in the Traveler when she didn't receive a package from her mother at the Pillow Trove. He manifested and reassured her, explaining that Jester's mother was unaware of her location at that moment.

After Jester had successfully defaced and made her getaway from the Hearth of the Allhammer in Zadash, he made his presence known by taking a bite out of the caramel apple she had been eating.

Located among the many religious artifacts found in the Merrow lair, Jester finds two different iterations of the Traveler symbol. Despite having zero knowledge of anyone else worshipping or acknowledging the Traveler, Jester excitedly goes around to show everyone her find.

Jester attempted an elaborate prank on the temple to the Platinum Dragon in Zadash that went off the rails and almost got Jester and Nott thrown in prison. Jester told the Traveler afterwards that she did it to get his attention after feeling abandoned when she was kidnapped. The Traveler claimed never to have abandoned her. The Traveler told her about a summit of his worshipers happening on the Zenith in Unndilar, and Jester promised to attend.

The Traveler appeared to Jester on the Squall-Eater to compliment her on her usage of Nolzur's Marvelous Pigments. When Jester asked him for advice on wooing Fjord, he noted that there were many enchantments he could teach her. He reiterated the planned summit of his followers, and asked Jester again to attend.

Trivia

 * The Traveler that Jester worships is not the same as the one in the Eberron setting of Dungeons & Dragons, as Matthew Mercer confirmed that they only share the same name. He also said that the Traveler may not necessarily be a god.
 * In the Dwendalian Empire, "worship outside the approved idolatry is met with imprisonment". The Traveler isn't one of the six approved deities and worshiping him is illegal, though most citizens of the Dwendalian Empire seem unaware of his existence.
 * A common theory in the fandom is that The Traveler is actually Artagan from the first campaign, given new power and influence in this dimension.  The theory goes that, after Vox Machina completed their end of their deal with him and built a doorway from the Feywild to Exandria, Artagan took on the role of The Traveler in the hopes of finding a path to godhood.  There is some evidence that is commonly cited, including:
 * Jester's drawings are frequently described in a style that is very reminiscent of Garmelie's (another form Artagan takes) preferred art style.
 * Jester's pranks resemble the pranks Garmelie had Vox Machina play as part of his deal when they entered Syngorn.
 * Artagan is commonly linked to the color green and the brief bit we've seen of The Traveler, the only physical description he is given is having green eyes.
 * The Traveler's symbol is that of an open doorway leading to a path, a possible connection to the doorway Vox Machina made for Artagan to crossover with.
 * His name is "The Traveler" implying he traveled from someplace else, potentially the Feywild.
 * The Traveler and Artagan are both powerful tricksters.