To me, I hear a lot of similarities and both had that suave thing down. It is possible that if he had lived, Sam would have gone in the What's Going on Direction that Marvin did

Sam influenced Marvin.

I'm not sure how much, if any, influence Marvin had on Sam. At the time of his death Sam was already an established star and much bigger than Marvin.

Regarding What's Going On, well, Sam was doing "socially conscious" music just before he died ("A Change Is Gonna Come), that was roughly six-seven years before Marvin started writing similarly themed songs.

I would say that Sam was almost certainly a big influence on Marvin and that Marvin was probably not an influence on Sam at all.

Yes Sam influenced Marvin, he was writing socially concious music before Marvin and wearing his fro when everyone of his era were still perming it.

Eh, I think of the only thing that Sam influenced Marvin was when he did What's Going On though I don't think he openly admitted it (and besides Curtis Mayfield was doing socially conscious material before Sam). Marvin was more influenced by Brook Benton and Little Willie John than Sam Cooke.

[Edited 11/2/12 21:39pm]