Mr. Mystery. Grunkle Stan embodies a lot of the humor from Gravity Falls – snark, cynicism, and relatable vulnerabilities expressed through emotional yelling.
There was always an uncomfortable question with Stan, though. He seems so simple and ignorant, but from the beginning it’s clear that he’s been keeping secrets. How is he able to seem so earnest in his skepticism while collecting journals in a hidden basement?
Season 2 gives a great answer: Stan had secrets, but they didn’t make him any less of a normal person. He collects journals, but barely understands what they’re for. His skepticism is a lie, but he genuinely thought it could convince Dipper and Mabel. He doesn’t have a fancy tattoo; he has a meaningless scar from a fight with someone he loved. It’s one of those ways that Gravity Falls makes sure its plot doesn’t take away from its character’s humanity, even as inhuman as the plot is.
At the end, Stan was a man abandoned by his family, who could never succeed. The reason he’s trusted with two kids is because he’s been confused with someone else (albeit someone less trustworthy with kids). He’s sad, and cynical, and greedy, but also tirelessly works towards making things right.
I’m drawn to people who constantly try to do good, and mess up every single chance along the way. Stan carries that in style.