Ah yes, I've ran into "The Sentinel"
The first time I remember is reading about him here on these forums, interested. So, I start a Madrazo mission and after it's done, here he comes speeding by and I unload my M4 into his car. He stops and tries to get out, only getting the rest of my magazine into his body. I forgot what he looked like, but he did have a gun on him. I still have his Sentinel XS, nothing too special about it, I was hoping it was the hardtop convertible version.
Second time I found him was actually finishing the Dirt Road mission getting Trevor's truck. After the mission end screen, I start walking to my car and here he comes again, driving fast by Trevor's trailer. Again, I unload a magazine into his car and him, this time he's a big, black, well dressed man with dreads, sporting a weapon. I take his car, again, nothing special about it.
Seriously, who is this guy? Is it some kind of mercenary that later will be explained in DLCs or just some joke from Rockstar? All I know is that it's giving me the spooks thinking of some random mercenary that everyone is seeing.