I dont get why u call the earlier bets with the aces on the board but fold on the river. If i was playing the hand i would have folded on the flop depending on the player and the read or if i didnt place him on the ace you gotta call all the way based on the board. I doubt he was holding pocket kings with a limp it seems to me that he had either a middle pair and limped not knowing how to act in early position and afraid of the reraise or possibly a marginal hand like kq or kj or suited connectors. To me it looks like a straight bluff but then again an low to middle ace 7 could also be a starting hand so u never know it could of been a hell of a fold