Was Iblees a Fallen Angel who Disobeyed God and Took 1/3 of the Angels with him?

No, Rather, Iblees was from Among the Jinn, he Defiantly Disobeyed Against his Lord, but the Angels do Not Disobey God, for they do what they are Commanded

And so When God Said to the Angels, "Prostrate to Adam," they Prostrated, All of them Entirely; for God is the Subjugator Over them, and so they do Not Fail in their Duties to Take you in Death, Nor to Record Whatever you do, Nor to Cast the Wicked into Hell

16:49 - 50, Qur'an
Whatever is in the heavens prostrates to God and whatever is on the earth of creatures, and the angels [as well], and they are not arrogant. They fear their Lord above them, and they do what they are commanded -

18:50, Qur'an
[And thus,] when We said to the angels, "Prostrate to Adam,"

38:73, Qur'an
The angels prostrated - all of them entirely.

18:50, Qur'an
Except for Iblees. [For] he was from the jinn and defiantly disobeyed against the command of his Lord.

38:77, Qur'an
[So God] said, "Then get out of it, for indeed, you are expelled."

38:82 - 83, Qur'an
[So Iblees] said, "By Your might, I will surely mislead them all, except for Your chosen servants among them."

38:84 - 85, Qur'an
[So God] said, "The truth [is My oath], and the truth I say - [that] I will surely fill Gehenna with you and those of them who follow you all together -

37:22 - 23, Qur'an
[For on the Day of Judgement, I will command the angels,] 'Gather those who committed wrong, their kinds, and what they used to serve other than God, and guide them to the path of Hellfire.'"

66:6, Qur'an
[So] O you who have believed, protect yourselves and your families from a Fire whose fuel is people and stones, which angels are [appointed] over, harsh and severe; they do not disobey God in what He commands them, but they do what they are commanded -

6:61, Qur'an
[For] He is the subjugator over His servants, and He [also] sends guardian [angels] over you until, when death comes to one of you, Our [angel] messengers take him, and they do not fail [in their duties] -

32:11, Qur'an
[For] the angel of death will [certainly] take you, who has been entrusted with you [by God].  Then you will be returned to your Lord.

47:27, Qur'an
[And so] how [will it be] when the angels take them in death, striking their faces and their backs?

16:28, Qur'an
The ones whom the angels take in death [while] wronging themselves, and [who] then offer peace, [saying], "We were not doing any evil." But, yes! Indeed, God is Knowing of what you used to do -

82:10 - 12, Qur'an
[For] indeed, there are guardian [angels appointed] over you, noble and recording; they know whatever you do.

43:80, Qur'an
Or do they think that We do not hear their secrets and their private conversations? Yes, [We do], and Our messengers are with them recording.

50:23 - 26, Qur'an
And [so on the Day of Judgement,] his companion, [the angel], will say, "This [record] is what is prepared with me." [Then God will say to the angels], "Throw every obstinate disbeliever into Gehenna, preventer of good, aggressor, and doubter, who made another god [as equal] with God; then throw him into the severe punishment."

Matthew 13:49 - 50, Gospel
[And thus,] will it be at the end of the world, the angels will come forth, and sever the wicked from among the just, and will cast them into the furnace of Fire, there will be wailing and gnashing of teeth -

8:50 - 51, Qur'an
[For] if you could see when the angels take the souls of those who disbelieved - they are striking their faces and their backs and [saying], "Taste the punishment of the Burning Fire. That is for what your hands have put forth [of evil] and because God is never unjust to His servants."