In Wikipedia he's named as the "Master of Tahull", and also on other sites that I've consulted.
Is there a record of his real name?
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Artists, most often from early periods, whose hand has been identified by art historians, but to whom no identity can be confidently attached, are often given names by art historians such as Master E.S. (from his monogram), Master of Flémalle (from a previous location of a work), Master of Mary of Burgundy (from a patron), Master of Latin 757 (from the shelf mark of a manuscript he illuminated), Master of the Brunswick Diptych or Master of Schloss Lichtenstein.
So it is not uncommon for an artist to be unknown and referred to by a title of a work they did or a location central to their works.
The relevant wiki entry for the Master of Taüll gives no hint to any possible identity. The book The Art of Medieval Spain, A.D. 500-1200 By Jerrilynn D. Dodds lists this individual as the Master of Sant Climent, for his primary mural in the apse of the church in Taüll. A discussion (pp. 194-5) compares this artist with another unknown, the Master of Santa Maria in Taüll, which illustrates how common unknown artists are.