I would say hero holds AA. He decided to slowplay it preflop. On the flop, however, due to the fact that it is quite wet, Hero decides to flat call villain's bet to keep his bluffs in. Same goes for turn and river. Suits really does not matter in this case, because on the flop Hero has to call!!! and on the turn he doesnt have any flush possibilities anyway, but if i were to guess I would say A 
A 
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Pocket Aces.
Preflop: since it's a zoom hand (ranges are tighter) I don't see UTG bluff 4betting oop with marginal hands like SC or small PP. Even with JJ he would have a hard time 4betting here. So I think his range is QQ+ and maybe AK. If UTG thinks hero is bluff 3betting, he would bluff 4bet more, that's why I rule out any bluffs.
Now lets think of the range Hero would 3bet/call here. I don't find many small PP in his range because Hero would prefer to call with them and keep the pot smaller, also inviting SB and BB to join the pot. SC - maybe as a bluff, and Hero may very well call a 4bet because UTG gives him good pot odds (3,6:1). QQ-KK - unlikely, since Hero would stack off with these hands preflop (well, mayyybe KK...). AA - yes! Since UTG has shown great strenght 4betting oop, it would be wise to trap him because he folds everything but KK to Hero's 5bet jam.
Flop: Hero calls, and I think we can narrow down his range to [AA, KK, 56s]
An alternative option: Hero has TT-QQ and is too intimidated to stackoff pre (or simply decides to setmine) but just can't fold an overpair postflop hoping to see AKs in UTGs hand. But I find this unlikely 
Turn: blank since we put UTG on a preflop monster. So call is a logical decision.
River: blank since we put UTG on a preflop monster. So call is a logical decision.
So, lets sum it up: as AA is far more likely than KK here, and PokerStrategy wouldn't promote calling down a 4bet with 56s ♦, there is only one hand left - AA.
Here's my guess:
Pocket pair of Aces, AA, probably AxA
Preflop:
3-betting for value is very common with such a monster made hand. Calling the 4-bet from UTG to get more value in the later street.
Flop:
Calling is common here, the odds for flushdraw with is 5:1 since Hero is holding A :diamond:.
Turn and River:
Flush cards didn't hit, calling is standard for optimizing value. Re-raising might cause UTG to fold.
AdKx
not enough to 5bshove, plays good postflop, F,T normal calls w/ 2OC + nutFD, calls R because it doesnt hit UTG range + blocks a lot of combos
I am thinking a pair of sevens as well because the hero does not raise at any point in the betting. Trying to get value for his trips and eventual boat would make sense.
A 4
Preflop: called 4bet because has a decent playability.
Flop: called because we would often face QQ+ and we beat his bluffs so we can just call flop and turn easily.
Turn: the same as flop
River: we missed flushdraw but have three of a kind and an easy call.
A A
I can't think other hands for Hero.
Preflop just flat the 4b because there is more value in that, than push. Postflop there is no reason to raise, let him bluff, if he wants to, or vbet weaker hands.
I'll go with K :diamond:K 
Hero has a bluffcatcher to call pre and call down, letting the villain bluff himself out. I'd say he will usually have a monster, like KK+, although it's possible he has JJ+ and even TT from time to time depending on dynamics.
So I'd guess KK+ and, since I have to narrow down to one hand, I'd say KK, maybe with K of diamonds. Hence, if I need to guess specifically two cards, I'd guess K :diamond:K
Ad4d
3bet and then call the 4bet preflop because of position.
Postflop we have FD so we call flop and turn and then we hit trips on the river so we have easy call.