Phelim Caoch O'Neill ( Irish Féilim Caoch Ó Néill) was a Prince of the Cenel nEogain from 1517 to 1542. He was the first son of King Conn Bacach O'Neill 1st Earl og Tyrone.
Conn came from a long line of Ulster kings and was known throughout all the O'Neill provinces as "The O'Neill" or the most supreme among all the O'Neill Lords. Phelim's mother was Lady Alice Fitzgerald, the daughter of Gerald FitzGerald, 8th Earl of Kildare. His father and maternal grandfather were probably the two most powerful men in Ireland in the 1540s.
Phelim was raised in the Gaelic fashion at the family castle in Dungannon in County Tyrone, and was groomed to one day be the King of Tir Eoghan himself. At the time of his birth, his uncle was King, but at his death in 1519, his father assumed the throne of Tir Eoghan, and the over-chiefship of all three O'Neill houses: Tir Eoghan, the Fews, and Clanaboy. He was the supreme ruler of all of Ulster. Phelim grew up learning the diplomacy and art of rule and war in northern Ireland. He took part in activities of his father's kingdom, including a stint as a hostage to the English just before his death. A part of Irish culture of that period was the custom of raiding. Raids against neighboring lords for cattle was a primary past time for young noblemen. Especially in Ulster, cattle was main element of wealth. Thus raiding punished or promoted a junior Lord in the O'Neill world. The O'Neills had a continuous series of battles with the Antrim Scots, led by the MacDonells. Followers of Phelim were named "Giolla Caoch".
This article on Prince Phelim has been "lifted" from Wikipedia. Although the connection with Giolla Caoch (or Mac Giolla Caoch)/Kilkie/Gilkie is tenuous, it is worthy of consideration of further research. Note that the term caoch was a common nickname given to people with bad eyesight or to blind, but it unlikely that anyone would be named a follower of someone who had no religious or secular notoriety? Note that Caoch could also be written as Caoic, but pronounced the same way.