Opp is unknown, should I fold to his river reraise (disregarding the great pot odds I'm given)?

Party Poker No-Limit Hold'em, $ BB (6 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

SB ($13.95)
BB ($97.69)
UTG ($43.56)
MP ($13.05)
CO ($171.74)
Hero ($98.50)

Preflop: Hero is Button with J, K. SB posts a blind of $0.50.
2 folds, CO calls $1, Hero raises to $5, 1 fold, BB calls $4, CO folds.

Flop: ($11.50) 4, A, K (2 players)
BB checks, Hero checks.

Turn: ($11.50) 5 (2 players)
BB bets $5, Hero calls $5.

River: ($21.50) J (2 players)
BB bets $20, Hero raises to $50, Hero calls $37.69.

Final Pot: $129.19