I know i must sound like a reall dumbass, but i dont actually know who the witch king is. Could someone please help me out here,
it would really help
it would really help

A mortal, Frodo, who keeps one of the Great Rings, does not die, but he does not grow or obtain more life, he merely continues, until at last every minute is a weariness. …e fades: he becomes in the end invisible permanently, and walks in the twilight under the eye of the dark power that rules the Rings. Yes, sooner or later – later, if he is strong or well-meaning to begin with, but neither strength nor good purpose will last – sooner or later the dark power will devour him.
I wrote an essay on this some years ago. You can find it here.
The evidence points to a Númenórean prince who lived during the reigns of Tar-Minastir, Tar-Ciryatan, and Tar-Atanamir. I suspect he was the royal governor of Umbar, which means he most likely received his Ring of Power while living in Umbar sometime during the early- or mid-eighteenth century of the Second Age (i.e., the first half of the 1700s). He and the other two Númenóreans with Rings of Power must have returned to Númenor for a time. He seems to have been a close advisor to both Tar-Ciryatan, who forced his father to resign early, and Tar-Atanamir, who rejected the Númenórean acceptance of death (cf. Aragorn’s acceptance of death in the Appendices of Return of the King) and defied a formal embassy from Valinor on his religious views.
From the evidence we have, I think we can say that he was probably born around 1650, participated in the Númenórean expeditionary force to help Gil-galad in 1700, served as governor of Umbar, after which he returned to Númenor. As a member of the royal house and possibly the younger son of a king, he would normally have lived about 400 years. If, like Bilbo, he showed no signs of age, extraordinarily long life, and unusual mental and physical vigor, his example would have encouraged Tar-Atanamir to defy the Valar: before he disappeared and returned to Middle-earth, he was no doubt recognized as long-lived even for a Númenórean, well beyond 400 years. Tale of Years says the Nazgûl first appeared in 2251; that suggests he returned to Middle Earth under Sauron’s dominion sometime between 2100 and 2150 in the Second Age.
If Glorfindel returned to Middle-earth in the 1600s of the Second Age to help the Eldar still in Middle-earth fight Sauron (that’s one of Tolkien’s explanations; though another is that he retuned with Gandalf sometime after 1000 in the Third Age), then Glorfindel probably knew the Lord of the Nazgûl not only as a living man, but as a good and noble man before he received a Ring of Power.
Elrond almost certainly knew him.
Remember what Gandalf told Frodo in “The Shadow of the Past” at the beginning of Fellowship of the Ring:Gandalf is describing the three Númenóreans who succumbed to Sauron’s Rings, and most particularly the one that became the Witch King, the Lord of the Nazgûl.
Lt Ivan, Isilmo might be too old for this task.Isilmo could be a favourable candidate because the year the rings were completed was the time around Tar Telperien who was a queen, so she shouldn't of had them, but her brother second in line might of received the ring.