Summary:

What I hope to show is that the angel of the bottomless pit is NOT the king of the army that emerges from the pit. Not that the pit, key, smoke are necessarily literal, but I account for the figures and context as saying that God, through his Messiah, is unleashing the armies of Rome on Jerusalem and the temple in judgment.

In Revelation 1 John claims to be an eyewitness (via an angelic tour) of God's visitation of judgment on the Jews of the first century (66-78 AD) for violation of their agreement with the LORD (the Torah):

[Rev 1:1-2, 9-11 NLT] 1 This is a revelation from Jesus Christ, which God gave him to show his servants the events that must soon take place. He sent an angel to present this revelation to his servant John, 2 who faithfully reported everything he saw. This is his report of the word of God and the testimony of Jesus Christ. ... 9 I, John, am your brother and your partner in suffering and in God's Kingdom and in the patient endurance to which Jesus calls us. I was exiled to the island of Patmos for preaching the word of God and for my testimony about Jesus. 10 It was the Lord's Day, and I was worshiping in the Spirit. Suddenly, I heard behind me a loud voice like a trumpet blast. 11 It said, "Write in a book everything you see, and send it to the seven churches in the cities of Ephesus, Smyrna, Pergamum, Thyatira, Sardis, Philadelphia, and Laodicea."

He also is provided with a glimpse of the event from the perspective beyond the clouds:

[Rev 4:1-2 NLT] 1 Then as I looked, I saw a door standing open in heaven, and the same voice I had heard before spoke to me like a trumpet blast. The voice said, "Come up here, and I will show you what must happen after this." 2 And instantly I was in the Spirit, and I saw a throne in heaven and someone sitting on it.

On the ground you have war, famine, persecution, martyrdom, prophets being beheaded, Jews living like animals in caves, wishing they were dead, etc. In seeing Jerusalem and the surrounding empire from the sky you realize that the reason that the Jews are losing despite the home town advantage and a massive army is because it is the time for Israel's visitation. The Romans are acting as God's instrument (as Assyria and Babylon had done before):

NLT Deut 32:

28 "But Israel is a senseless nation; the people are foolish, without understanding. 29 Oh, that they were wise and could understand this! Oh, that they might know their fate! 30 How could one person chase a thousand of them, and two people put ten thousand to flight, unless their Rock had sold them, unless the LORD had given them up?

YHVH explains that in the latter days He will be at war with Israel and will make Israel's enemy army supernaturally effective at defeating Israel):

NLT Deut 32:

31 But the rock of our enemies [IE: apostate Israel's rock, which is Baal or some other deity] is not like our Rock [IE: the Rock of the heavenly armies, which is Christ], as even they recognize. 32 Their [IE: apostate Israel's] vine grows from the vine of Sodom, from the vineyards of Gomorrah. Their grapes are poison, and their clusters are bitter. 33 Their wine is the venom of serpents, the deadly poison of cobras.

This is the divinely designed day of vengeance is for their last days. "In due time" it will arrive:

NLT Deut 32:

34 "The LORD says, 'Am I not storing up these things, sealing them away in my treasury? 35 I will take revenge; I will pay them back. In due time their feet will slip. Their day of disaster will arrive, and their destiny will overtake them.'

Jonah's experience and others inform us that this dire prediction is not in and of itself necessarily void of hope that Israel might repent and receive their king:

[Rom 11:15 NLT] 15 For since their rejection meant that God offered salvation to the rest of the world, their acceptance will be even more wonderful. It will be life for those who were dead!

However, time was quickly running out because God had set a limit one final generation:

[Luk 13:1-9 NLT] 1 About this time Jesus was informed that Pilate had murdered some people from Galilee as they were offering sacrifices at the Temple. 2 "Do you think those Galileans were worse sinners than all the other people from Galilee?" Jesus asked. "Is that why they suffered? 3 Not at all! And you will perish, too, unless you repent of your sins and turn to God. 4 And what about the eighteen people who died when the tower in Siloam fell on them? Were they the worst sinners in Jerusalem? 5 No, and I tell you again that unless you repent, you will perish, too." 6 Then Jesus told this story: "A man planted a fig tree in his garden and came again and again to see if there was any fruit on it, but he was always disappointed. 7 Finally, he said to his gardener, 'I've waited three years, and there hasn't been a single fig! Cut it down. It's just taking up space in the garden.' 8 "The gardener answered, 'Sir, give it one more chance. Leave it another year, and I'll give it special attention and plenty of fertilizer. 9 If we get figs next year, fine. If not, then you can cut it down.'"

[Hos 9:10 KJV] 10 I found Israel like grapes in the wilderness; I saw your fathers as the first-ripe in the fig tree at her first time: [but] they went to Baal-peor, and separated themselves unto [that] shame; and [their] abominations were according as they loved.

[Hos 9:10 KJV] 10 I found Israel like grapes in the wilderness; I saw your fathers as the firstripe in the fig tree at her first time: [but] they went to Baalpeor, and separated themselves unto [that] shame; and [their] abominations were according as they loved.

[Mat 21:19 KJV] 19 And when he saw a fig tree in the way, he came to it, and found nothing thereon, but leaves only, and said unto it, Let no fruit grow on thee henceforward for ever. And presently the fig tree withered away.

This is describing the war:

[Rev 12:9-10 NASB] 9 And the great dragon was thrown down, the serpent of old who is called the devil and Satan, who deceives the whole world; he was thrown down to the earth, and his angels were thrown down with him. 10 Then I heard a loud voice in heaven, saying, "Now the salvation, and the power, and the kingdom of our God and the authority of His Christ have come, for the accuser of our brethren has been thrown down, he who accuses them before our God day and night.

The accusers are the Jews, being expelled from Jerusalem, their covenant negated and their temple destroyed. Over a million Jews died of hunger and exposure and such.

In the first chapter of Isaiah God shows that he thinks the Israeli theocracy is NOT a source of pleasure to God but rather a lightning rod for his wrath. He shows that he views them as just as toxic and abominable to him as Sodom and Gomorrah ever were and their fate will be the same:

[Isa 1:2-10 NASB] 2 Listen, O heavens, and hear, O earth; For the LORD speaks, "Sons I have reared and brought up, But they have revolted against Me. 3 "An ox knows its owner, And a donkey its master's manger, [But] Israel does not know, My people do not understand." 4 Alas, sinful nation, People weighed down with iniquity, Offspring of evildoers, Sons who act corruptly! They have abandoned the LORD, They have despised the Holy One of Israel, They have turned away from Him. 5 Where will you be stricken again, [As] you continue in [your] rebellion? The whole head is sick And the whole heart is faint. 6 From the sole of the foot even to the head There is nothing sound in it, [Only] bruises, welts and raw wounds, Not pressed out or bandaged, Nor softened with oil. 7 Your land is desolate, Your cities are burned with fire, Your fields--strangers are devouring them in your presence; It is desolation, as overthrown by strangers. 8 The daughter of Zion is left like a shelter in a vineyard, Like a watchman's hut in a cucumber field, like a besieged city. 9 Unless the LORD of hosts Had left us a few survivors, We would be like Sodom, We would be like Gomorrah. 10 Hear the word of the LORD, You rulers of Sodom; Give ear to the instruction of our God, You people of Gomorrah.

It is on the Lord's Day that John watches from the ground and from the throne room and the one being visited upon is the same apostate Israel as Isaiah cried against:

[Rev 11:8 KJV] 8 And their dead bodies [shall lie] in the street of the great city, which spiritually is called Sodom and Egypt, where also our Lord was crucified.

Now, with all these colliding images of what Rome will do and what Michael/Jesus and the heavenly army do and God behind it all it is hard to pick the passage apart to tell who opens the pit because I believe it represents in different images, the Messiah sending the Roman army to destroy the Jews.

• the angel with the key is Rome unleashing its army is the stuff coming out of the pit
• the angel with the key is also Jesus/Michael unleashing the heavenly army - because they are cooperating
• Israel is the "Satan" that has been the adversary against the new covenant Jews!