I don't think he exists yet. Current statements indicate he'll be in the next Patreon update, but that still means those of us playing the public version have a couple updates to go before we get him.
Late reply but the game's page features characters mostly to look forward to as the game continues to update as you can see with most of the sketched designs. We'll see them pop up eventually but it will likely take some time. As for Boulder, they'll be in the next Patreon update so for public builds, we'll get to meet him next-next update.
