Top five warriors of Yulin.
The martial artists of Yulin began calling the five strongest warriors of the entire Yulin and addressed them as such. It wasn't sure why the number limited to five, but these five figures became like tradition in Yulin's history. North Justice, South Demon, East Challenger, West Strong, and Middle Double.
North Justice Blade, Yi Mok.
South Demon Lord, Chun Yujong.
East Challenger God, Ark Wui.
West Strong King, Hang Yen.
Martial Dual Sword, Wang Jing.
North Justice Blade Yi Mok was the leader of the Yulin clan, and the clan leader of the Justice clan. Justice clan wasn't one of the Nine Great Clans, but historically they had many of the strongest warriors in the Forces of justice.
As for South Demon Lord, it originally addressed Chun Inji, but after defeating Alliance of Forces of Evil at Sawon Plains battle, Chun Yujong succeeded the name.