Jeong Cheol
Jeong Cheol was fired with most of the Westerners in 1590, the Easterners differed on whether they should kill or just exile Jeong. Most of the Easterners who wanted to kill Jeong lived near Mount Bukak (translated to the "Northern rock"), while most of the Easterners who opposed killing Jeong lived near Mount Nam (translated to the "Southern mountain"). The location caused those who wanted Jeong's death to be called the 'Northerners', while those who opposed his death became called 'Southerners'.