river spot vs unk #1

1/3 $1.1k effective. im doing my usual thing which is being a nit.

middle aged gent opens $15, 3 callers, i $75 OTB with AsKc, opener folds, other callers call pot $300

flop Kh8x2x rainbow, checked me me i bet $100, first cold caller calls, others fold pot $500. im not sure if i like this bet or not, maybe checking is better. anyways...

turn Ah he checks i check. i dont see what i get value from here so i decide to trap because i think Kx folds to a bet and sets stack me.

river Th. he shoves all in $600 after like 5 seconds.

i sneak a glance his way and he looks at me briefly then looks the other way. looks strong to me. villain is in his 20s.

call or fold?