Who are the guys in the portraits?

Portraits of Von Braun litter the walls of Alphaville.
However, there are also a couple of instances of framed photo portraits of individuals who look like candidates for a book of 100 greatest thinkers.
There is one sequence in particular, near enough the beginning; Lemmy asks a receptionist if they know who the photo on the wall is and they reply 'Of course'. There is a musical crescendo as the camera rests on the photo of Von Braun, but then silence as we follow Lemmy down the stairs. On the stairwell is a photo of a dude with a splendid beard, that I first thought to be Karl Marx, but now I'm not so sure. I'm thinking now that it's most likely to be a famous physicist or mathematician, but I'd love to know for definite.

There is also one other portrait of another chap later in the film (somewhere in the Semantics office I think)

Any ideas?