Cal Hampton
An online conspiracy hobbyist whose ideal night is beer, a scanner tuned to Coast Guard traffic, and a lot of open browser tabs.
Cal is the game's resident paranoiac: an online conspiracy hobbyist who listens in on Coast Guard communications for fun and treats the internet as a primary source.
He sits in the same circle as Brian and Jason, and is spotted at The Rusty Anchor bar, which is how a man whose main activity is staying indoors ends up adjacent to smuggling work.
The useful idiot, possibly
It is worth noticing what his hobby actually is. A man who monitors Coast Guard radio around the clock, in a group of people who move product by boat, is sitting on operationally useful information whether or not he understands that. Rockstar has not said this is his function in the story. It would be a very Rockstar joke if the group's early warning system did not know he was the early warning system.
Why the character exists now
Grand Theft Auto has satirised American media in every entry, and the target has always been whatever was dominant at the time. San Andreas had talk radio. Grand Theft Auto IV and V had cable news, reality television and the first wave of social media. A game set in the present day has to deal with the fact that the loudest media environment in America is now a man in a room with a scanner and forty tabs open, convinced he has worked something out.
Cal is that, and the series has generally been sharper when its satire is embodied in somebody you have to spend time with rather than delivered through a radio station you can switch off.
The voice actor question
His casting is not settled. Different outlets have named Bobby Moynihan and Matty Matheson. Rockstar has never published a cast list for this game, so treat both as speculation until it does. We are noting the disagreement rather than picking a side, because a confident answer here would be somebody else's guess repeated with more conviction.
What is not known
How much mission time he gets, whether he is a friend, a contact or a problem, and what he actually knows have all been kept back. He has been shown as texture so far rather than as a job giver.