Hello Rosie. Any angel making a deal with the Devil would become a demon or fallen angel. I suppose that sense devil means slanderer and demons slander Jehovah, all demons can be called devils but the Bible refers to them as demons. There is one fallen angel in particular that is referred to as the Devil. I suppose that he may possibly be more evil than the others? although they are all evil. Apparently he was initially in the garden looking over Adam and Eve until he desired to be worshiped by them?
(Ezekiel 28:13-16) You were in Eʹden, the garden of God. You were adorned with every precious stone —Ruby, topaz, and jasper; chrysʹo·lite, onyx, and jade; sapphire, turquoise, and emerald; And their settings and mountings were made of gold. They were prepared on the day you were created. 14 I assigned you as the anointed covering cherub. You were on the holy mountain of God, and you walked about among fiery stones. 15 You were faultless in your ways from the day you were created Until unrighteousness was found in you. 16 Because of your abundant trade, You became filled with violence, and you began to sin. So I will cast you out as profane from the mountain of God and destroy you, O covering cherub, away from the stones of fire.
(Zechariah 3:2) Then the angel of Jehovah said to Satan: “May Jehovah rebuke you, O Satan, yes, may Jehovah, who has chosen Jerusalem, rebuke you! Is not this one a burning log snatched out of the fire?” (Jude 9) But when Miʹcha·el the archangel had a difference with the Devil and was disputing about Moses’ body, he did not dare to bring a judgment against him in abusive terms, but said: “May Jehovah rebuke you.” (Revelation 12:9) So down the great dragon was hurled, the original serpent, the one called Devil and Satan, who is misleading the entire inhabited earth; he was hurled down to the earth, and his angels were hurled down with him.
Devil. The descriptive name of Satan in the Christian Greek Scriptures, which means “Slanderer.” Satan was given the name Devil because he is the chief and foremost slanderer and false accuser of Jehovah, His good word, and His holy name.—Mt 4:1; Joh 8:44; Re 12:9.