Don't go with sports stars or actors - there are always going to be demographics who don't give a shit about that stuff. Like Lionel Messi is only someone I've really only come to know by face in the past couple years because I don't care about soccer.
With that in mind, I really can't think of a single demographic in the world (who has access to television or internet) that wouldn't know Obama's face. Seriously, if you showed a picture of Obama to damn near anyone in the world and they didn't know who he was, wouldn't you be kind of shocked? An iconic face with iconic features that's not just a haircut. Obviously his job helps.
With that in mind, I really can't think of a single demographic in the world (who has access to television or internet) that wouldn't know Obama's face. Seriously, if you showed a picture of Obama to damn near anyone in the world and they didn't know who he was, wouldn't you be kind of shocked? An iconic face with iconic features that's not just a haircut. Obviously his job helps.