There is no angel named Gadreel in the Bible. The idea of an angel named Gadreel comes from the mythical and apocryphal Book of Enoch.
Much of the content of the Book of Enoch deals with angelology and demonology, and a large portion of the book is devoted to filling in the backstory of Genesis 6:1–4. The Book of Enoch thus goes into great detail explaining the origin of the Nephilim, mentioned in Genesis 6:4, and the identity of the “sons of God,” mentioned in verses 2 and 4. The result is a strange and sensationalistic work of non-canonical literature.
According to the mythology contained in the Book of Enoch, Gadreel was one of 200 Grigori, or watchers, who rebelled against God and were cast out of heaven along with Satan. Gadreel was the third of five leaders of the Grigori. He and other angelic leaders were instigators of a vile sin, prompting other fallen angels to indulge their lust and have sexual relations with human women. The result of these unnatural unions was the Nephilim, a race of evil giants who terrorized the antediluvian world. A judgment was then pronounced upon Gadreel and the other demonic watchers.
According to Jewish mythology, another of the Grigori besides Gadreel involved in fornicating with human women and producing a race of giants was Azazel, a goat-like demon associated with the wilderness and desert places.
The Book of Enoch describes some of Gadreel’s other supposed activities: “And the third was named Gâdreêl: he it is who showed the children of men all the blows of death, and he led astray Eve, and showed [the weapons of death to the sons of men] the shield and the coat of mail, and the sword for battle, and all the weapons of death to the children of men. And from his hand they have proceeded against those who dwell on the earth from that day and for evermore” (Chapter LXIX, verses 6–7, trans. by Charles, R. H., 1917).
So, according to the legend of the Book of Enoch, all warfare can be traced back to Gadreel, who taught mankind how to kill and helped them develop weaponry. On top of that, he is the serpent who tempted Eve and caused her to fall into sin.
The Bible does not give us much information about the holy angels, and even less about the fallen angels. Besides Satan, few names of fallen angels are revealed to us. We know next to nothing of demonic rankings, names, or abilities. Elaborate and complicated stories about spirit beings supposedly named Gadreel, Azazel, Penemue, etc., are nothing more than the products of human imagination. The only reliable source for information about angels and demons is inspired Scripture.