East Heretic Wong Yerk See was characterized as inclined to wear a mask when out in public (perhaps for no other reason than his being eccentric). Dependng on what adaptations of LOCH or ROCH you go by, however, the mask takes on a number of different guises. In LOCH '82, it was a red devil mask with horns. In some later adaptations, the mask was a "Phantom of the Opera" style mask. Some versions, I think, even give him one of those "human skin" masks.
But did Jin Yong himself ever describe the mask? Why did Wong Yerk See wear it (other than being eccentric)? Did he stop wearing it after a time?