Villain is a winning player. I don't think he is very good, but my standards for calling a player very good are quite high. I don't really have much of a read beyond that. So basically just assume a thinking TAG.

PokerStars Game #15282836858: Hold'em No Limit ($2/$4) - 2008/02/14 - 13:55:57 (ET)
Table 'Brown II' 6-max Seat #4 is the button
Seat 1: Xaston ($963.50 in chips)
Seat 2: Arlequin333 ($634.25 in chips)
Seat 4: serraios36 ($109.05 in chips)
Seat 6: felted-away ($721.30 in chips)
felted-away: posts small blind $2
Xaston: posts big blind $4
*** HOLE CARDS ***
Dealt to Xaston [Ah Ac]
Arlequin333: folds
serraios36: raises $4 to $8
felted-away: raises $16 to $24
Xaston: raises $75 to $99
serraios36: folds
felted-away: calls $75
*** FLOP *** [Td Kh Tc]
felted-away: checks

What are we putting him on and what is our plan for the rest of the hand?

I would check it back as well.

Well, imo he can have KK for sure. But also QQ and AK, possibly JJ or the vague chance of TT (which can be neglected).

Pot should be something like 200+, so I'll fire maybe 70 at it. If he calls, I'm worried. I guess I'll have to call one raise here. But if he calls and checks turn, I'm checking behind on turn, then calling a reasonable river bet. You can obviously beat AK or a bluff, but I'd try to keep this pot as small as possible while not going away and giving him an opportunity to fold on the flop.