Nothing is known for certain about this artist, except that he was working in Ferrara about 1441. It is possible that Nicholaus was the Nicholaus Teutonicus (Niccolò d'Alemagna) who is known to have painted a portrait in 1454 of Beatrice, the illegitimate daughter of Niccolò III d'Este, shortly before her marriage to Tristano, the son of Francesco Sforza. Niccolò d'Alemagna may have been both a painter and a medalist, because the Milanese agent at Ferrara, in writing to the court at Milan, said that Niccolò "il ve retrara naturale et mettear la figura o vero effigie vostra in medaglia" (he will portray you from nature and put your figure or rather effigy on [a] medal).[1] Nicholaus seems to have been employed at Ferrara as early as 1440 and was active until about 1454. Only one medal is signed by him, of Leonello d'Este, and two are attributed to him, of Leonello d'Este and Antonio Pisano, called Pisanello (NGA 1957.14.622).
[1] Emilio Motta, "Il Pittore Baldassare da Reggio (1461-1471)," Archivio Storico Lombardo 16 (1889): 404 n. 3.
[This is the artist's biography published in the NGA systematic catalogue of Renaissance medals.]