King of the North is Russia and allies, primarily China, but all the brics nations. (Brazil Russia India China and South Africa
In JW doctrine, the "king of the north" is usually only Russia (but also described as Russia and its allies in a 2020 Watchtower article), but Russia and its allies (but sometimes suggested as being all nations) are 'Gog of Magog'. See also Daniel's dreams and visions (Appendix 2), Pure Worship—Ezekiel revisited (Chapter 17).
Back in reality, the "king of the north" was the dynasty of Seleucid kings up until Antiochus IV. See Daniel's dreams and visions (Chapter 11).
'Gog of Magog', entirely unrelated to the "king of the north", was a hypothetical ruler from the far north of Israel who would purportedly lead an attack against Israel some time after the fall of Babylon. See also What Does the Bible Really Teach… about Gog of Magog? (PDF).