Nicholas Eudaimonoioannes

Nicholas Eudaimonoioannes (Greek: Νικόλαος Εὺδαιμονοϊωάννης) was a Byzantine senior official of the early 15th century, most notable as ambassador to the Papacy during the Council of Constance and to the Republic of Venice during several occasions.

Nicholas is perhaps the best-known member of the noble Eudaimonoioannes family, or at any rate the one about whom most reliable information survives. Based on a manuscript colophon variously dated to either 1415/16 or 1419/20 he was a "synpetheros" of the Emperor Manuel II Palaiologos, implying a relation by marriage. What this relation was is unknown, although the Greek historian Haris Kalligas has suggested that his son George may have married a daughter of Manuel II sometime shortly after 1415.

Nicholas is first mentioned, along with his wife and children—who are not named—in an epitaph now in the Victoria and Albert Museum, dated to 1407. In the same year, he was appointed as tutor and regent over the young Theodore II Palaiologos, who was appointed Despot of the Morea. Nicholas probably bore the title of megas stratopedarches, although this is attributed by some modern sources to his son George.

As he knew the languages spoken in Western Europe, Nicholas was appointed as the head of a Byzantine delegation to the Council of Constance in early 1416. According to Ulrich von Richental, he was accompanied among others by his otherwise unknown son Andronikos ("Andriuoco von der Morea"). The Byzantine envoys first visited Venice in February, where they offered to mediate for the conclusion of peace between the Venetian Republic and the King of Hungary, Sigismund, but also asked for aid in rebuilding the Hexamilion wall that protected the entrance to the Morea, and urged the formation of a Christian league against the Ottoman Empire. The Venetian Senate gladly welcomed the Byzantine proposal to mediate with Sigismund, but was reluctant to commit itself on either of the latter proposals. The Byzantines arrived at Constance on 25 March 1416 and remained there for over a year, with Nicholas assisting at the election and investiture of Pope Martin V in 1417. On Nicholas' request, the new Pope gave permission for the marriage of Manuel II's two sons to Catholic princesses.

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