I'm a bit confused about some of the answers and comments on here, so I'd like to try and answer the question and also address what has already been written. If I'm wrong, I would greatly appreciate if somebody would help clarify why. Thank you.
καὶ (and)παρήγγειλεν (he instructed) ἡμῖν (us) κηρύξαι (to proclaim) τῷ (to the) λαῷ (people) καὶ (and) διαμαρτύρασθαι (to testify fully) ὅτι (that) οὗτός (he) ἐστιν (it is) ὁ (the) ὡρισμένος (having been determined) ὑπὸ (under [the authority]) τοῦ (of the) Θεοῦ (God) Κριτὴς (judge) ζώντων (of living) καὶ (and) νεκρῶν (of dead)
The question concerns who is the judge of the living and of the dead- the "one determined" or God. I am under the impression that God is the judge, and the verb ὡρισμένος is functioning intransitively. I would translate this verse as:
And he instructed us to proclaim to the people and to testify fully that he it is having been determined under God- judge of the living and of the dead.
First is whether "judge" should be in the genitive if the author of Acts wanted to say God is the judge, since τοῦ Θεοῦ is in the genitive. This would make verse say:
"...he it is having been determined under [the authority] of God of judge of the living and of the dead."
The reason τοῦ Θεοῦ is in the genitive is because of the preposition ὑπὸ, which literally means "under" and metaphorically "under the authority", so it is translated in English as "by":
with the genitive (cf. Winers Grammar, 364 (342), 368f, (346); Buttmann, § 147, 29), it is used:
properly, in a local sense, of situation or position under something higher, as ὑπό χτονος, often from Homer down; ὁ ἐπί γῆς καί ὑπό γῆς χρυσός, Plato, legg. 5, p. 728 a.; hence,
metaphorically, of the efficient cause, as that under the power of which an event is conceived of as being; here the Latin uses ἆ or ἀβ, and the English by; thus a. after passive verbs
So Κριτὴς does not need to be in the genitive to correlate it with God.
The second issue involves what the author of Acts could have said as opposed to what he actually said. Because Κριτὴς is in the nominative, it is the subject of the phrase "judge of living and of dead". If the author wished to make Κριτὴς the direct object of the verb ὡρισμένος, he would have used the accusative κριτήν. That is correct grammar.
The reason ὡρισμένος is passive is because the subject "he/Yeshua" is being acted upon by God as "the one having been determined".
This is all important for two reasons. The first is because Yeshua specifically tells us:
"And if any man hear my words, and believe not, I judge him not: for I came not to judge the world, but to save the world.
He that rejecteth me, and receiveth not my words, hath one that judgeth him: the word that I have spoken, the same shall judge him in the last day." John 12:47
And John tells us:
"For God sent not his Son into the world to condemn (κρίνῃ- judge) the world; but that the world through him might be saved." John 3:17
Since Yeshua is not the judge, and God is the judge, Peter would have no reason to say Yeshua has been appointed the judge.
The second reason has to do with the next sentence in Acts:
"To him give all the prophets witness, [that] through his name whosoever believeth in him shall receive remission of sins." Acts 10:43
Since the author has changed the subject from Yeshua to God, then the first ""him"" would make more sense as referring to YHVH rather than Yeshua.
"To him (YHVH) the prophets testify. Because of (διὰ) his name (Yeshua- YHVH Saves), whoever believes in him (YHVH) recieves remission of sins."
This makes a lot more sense, especially since translations like to say that...
"...the prophets testify that through his name..."
...when no prophet ever said this.
Again, if I've misunderstood anything, I would really appreciate correction. Thank you.