My first thought was also bullmastiff. I think he at least has quite a bit of it in him, though there may be more breeds than that in his history. He isn't as "extreme" in his features as a bullmastiff, so I think he's either a mix or just a badly bred bullmastiff.
He looks like a sweetheart.
My old Rottweiler Harley used to sit in my lap like that.
He looks like a sweetheart.
My old Rottweiler Harley used to sit in my lap like that.