...shouldn't he have some weight to throw around? Shouldn't he have the respect and trust of a 20 year tenured employee? Shouldn't he be able to bring this up with his boss and put him in his place? If not, perhaps he's not as valuable or skilled as you say he is. Or perhaps he has a poor boss. Or perhaps the culture at the company sucks. But something isn't adding up.
Also, judging by the behavior of his supervisor it sounds like he's definitely younger than your FIL. My question is this. Shouldn't your FIL be the supervisor by this point?