Each generation of wulin in Jin Yong's universe has its "director" or leader. Sometimes, this individual is the most powerful fighter in the wulin of his era, but this is not necessarily true. More important is that this person has the respect of wulin and that others will follow his directives. Let's do an inventory (you guys will need to supplement the novels I'm not familiar with):
DGSD: It would seem to have been the Chief Abbot of Shaolin (Yeun Chi). Shaolin seemed to be the central wulin organization in the Central Plains at the time. There were more powerful fighters than the Chief Abbot, and certainly Kiu Fung and the Mo Yung Family were more notorious. Since those figures were more controversial, however, the role of Wulin Director in the DGSD era went to Chief Abbot Yeun Chi (until, of course, his own very controversial dark secrets came to light). After his death, however, there seemed to be no obvious successor for Yeun Chi as Wulin Director.
Pre-LOCH: Central Divinity Wong Chung Yeung, no doubt.
LOCH: There were four Greats, each of equal prowess in the martial arts and each commanding a high degree of respect in wulin. There didn't seem to be a cut and dry Wulin Director among the four, but it leans towards North Beggar Hung 7 Gung if only because he was the Chief of the Beggar's Union and the Great most readily characterized as a hero. Such a title or role never went to any of the four Greats of the LOCH era, however.
ROCH: Initially, there was none. After the Heroes Conference at Dai Sing Kwan, however, it was clearly Gwok Jing.
HSDS: It was evidently Cheung 3 Fung. After the Battle of Gwong Ming Peak and the resurgence of the Ming Cult, however, Cheung Mo Gei seemed to become the de facto Wulin Director.
SOD: I'd say it was Dong Fong But Bai and after his/her demise, Ngok But Kwun. Dark times.
DOMD: Wulin was such a chaotic mess at this time. Could it have been Chan Jen Nam?
B&S: G&R: Chan Ga Lok, I suppose. By the Qing Dynasty, the very concept of Wulin Director seemed to have become antiquated.