I read years ago that during WW2 there was a move to create a new rank in the US Army because the four star General George C Marshall was visibly outranked by, say, a British Field Marshal (five stars). The new US rank was to be "Marshal". It appears that GCM torpedoed the proposal, on the grounds that there was just no way he was ever going to be "Marshal Marshall".
Incidentally, and subject to checking, I think the highest rank attained during his service by Ulysses S Grant was lieutenant general.