What king was instrumental in tightening the grip on Ireland?

Answer 1

Although many kings had their forces in Ireland with varying degrees of success and interest, the real push to subjugate the entirety Island wasn't carried out by a King at all. It was undertaken by Queen Elizabeth. Many areas capitulated rather quickly either through bribes or massive force. Ulster, however, would not go as quietly and managed to hold off the Queens army for a few years using guerrilla tactics. They also managed to gain more land by using their guerrilla tactics and spreading into the Connacht area. The Spanish sent an expeditionary force to aid the Irish at which time the Ulster troops switched to more formal military tactics. Of course they were not trained in formal military tactics and as a result suffered a major defeat. The queen�s forces were able to push them back to Ulster. About two weeks after the death of Queen Elizabeth the leaders of the Ulster troops surrendered. The leaders were allowed to keep their lands and titles but unwilling to live with British rule they fled from Ireland and never returned.