Of Khamûl very little is said, but for the fact that he was "The second in command", and must obey the Lord of the Nazgûl and The Dark Lord himself.
Komûl was born in the easternmost Endor in the year 1744 S.A., as the eldest son of Mûl Tanûl, who was the high Lord of the Womaw. He was first heard of around the year 2000 S.A., and at this time he had adopted the pronounciation of his name in the Black Speech, and went by the name Khamûl. At this time he was also the Lieutenant of Barad-Dûr, administering such tasks as the maintenance of the Citadel and its garrison. This wardship he held until the year 3350 S.A. when Ûrzahil of Umbar became the Mouth of Sauron and the Lieutenant of the Tower.
Khamûl left Mordor when Sauron was captured in 3262 S.A., but returned to his master in Barad-Dûr, in the year 3400 S.A. Here he stayed during all the Last Alliance, at the end of the war, and when the Dark Tower fell, he defended his master, and met the elven forces, in the year 3441 S.A. After this last stand of the Dark Lord and his servants it was over 1000 years before they were again heard of.
When Sauron reappeared, Khamûl resided for a short time with his master, in Dol Guldur in southern Mirkwood, where they rebuilt their strength. Later Khamûl and the 8 other Ringwraiths took Minas Ithil, and with it, the Palantír. From this time on they resided permanently in Minas Ithil and it was therefore called Minas Morgul.
Khamûl rode with the 8 other Ringwraiths to find the Ring, and soon came to the Shire. It was Khamûl's keen sense of smell that almost uncovered Frodo and Sam, in Green Hill County. Following the defeat at the ford at Rivendell, Khamûl returned to Dol-Guldur, and prepared for the war, from there.
Khamûl found his end along with Sauron at the of the War of the Ring, of which much more is told in J.R.R. Tolkien's The Lord of The Rings.
J.R.R. Tolkien Node