Trịnh Kiểm
The reason Trịnh Kiểm appointed Nguyễn Hoàng to the Southern provinces is not clear. As anecdote goes, Trinh Kiểm, being afraid of losing power to Nguyễn brothers, ordered the assassination of Nguyễn Hoàng's older brother. As for Hoang, Trịnh Kiểm wanted to take advantage of Mạc's southern garrison troops to eliminate his brother in law.