For an Informed Love of God
ὅς means “who (whom).”
I send my messenger ahead of you, ὅς will prepare your way” (Matt 11:10).
Mounce's Expository Dictionary (abridged):
Pronoun: ὅς (hos), GK G4005 (S G3739), 1,407x. ὅς is the relative pronoun meaning “who, which, what, that.”