Individual tal represent different characters from the plays. This particular mask is Choegwari, the old apostate Buddhist monk.
During the Koryo period, many Buddhist clergy held considerable political power. Corruption was rampant, and the high monks indulged not only in feasting and bribe-collecting, but also in the pleasures of wine, women and song. Thus, the corrupt and lusty monk became an object of mockery for the common people in talchum.
In the different plays in which he stars, Choegwari is shown feasting, drinking and reveling in his wealth. The fullness of his chin shows that he loves food. He also becomes enamoured of the aristocrat's flirty concubine, Bune, and carries her away. In one scene, we find Choegwari appearing out from under the girl's skirt, in a shocking violation of his monastic vows.
Incidentally, to western eyes the red color of this mask makes Choegwari appear somewhat demonic, but that is not the Korean interpretation. In many regions, white masks represented young women (or occassionally young men), red masks were for middle-aged people, and black masks signified the elderly.
The Universality of a Good Plot
Korean masked dance and drama revolves around four dominant themes, or plots.
The first is mockery of the avarice, stupidity, and general unwholesomeness of the aristocracy.
The second is the love-triangle of a husband, a wife, and a concubine.
The third is the depraved and corrupt monk, like Choegwari.
The fourth is a general good versus evil story, with virtue triumphing in the end. In some cases, this fourth category describes plots from each of the first three categories, as well.
These plays (in translation) would probably have been quite popular in the Europe of the 14th or 15th century, as well. These themes are universal to any stratified society.