Just a thought I had. Maybe ten years ago, I was running a D&D campaign for a friend of mine. At that time, it was just us. He ran a thief. We had a blast.
He planned out missions and even recruited a few NPC hirelings, that he used as look-outs. The game involved some heists and a few murders for hire. Politics started featuring later on, as well.
It was kind of like a Shadowrun game, but without guns or cybernetics. I had set the campaign in the kingdom of Mieres in the Birthright setting. The PC was not blooded, which worked out well. Mieres was the kingdom on the southwest corner of the map on the other continent, and was famed for thieves.
In any case, if you are running a game for only one player, I think thieves are a really good fit.