Villain is complete unknown.

PokerStars No-Limit Hold'em, $0.50 BB (6 handed) Poker-Stars Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

UTG ($52.75)
MP ($59.80)
CO ($32.85)
Button ($49.25)
Hero ($49.50)
BB ($43.35)

Preflop: Hero is SB with K, K.
2 folds, CO calls $0.50, Button calls $0.50, Hero raises to $3.5, 1 fold, CO calls $3, Button calls $3.

Flop: ($11) 2, 4, 5 (3 players)
Hero bets $8, CO folds, Button raises to $18, Hero