Medieval heraldry did not limit itself to the heraldry of existing individuals, families and entities. The notion that heraldry did not begin before the 12th century does not become clear to heraldists until the 17th century, and it seemed perfectly normal to attribute arms to individuals belonging to the pre-heraldic era. Another source of imaginary heraldry were novels or romances, whose fictitious characters were given arms. To this latter category belongs Arthurian heraldry, that is, the arms attributed to the knights of the Round Table and other characters appearing in various Arthurian legends and cycles.
The story of the Iliad was quite popular in the 13th century, with numerous versions in vernacular circulating (e.g., le roman de Troie). Arms are attributed to some characters.
The original romance, written by Benoît de Sainte-Maure c1150-60, was le roman de Troie, and it contains some coats of arms. For example, Cicinalor ("Escu ot d'or bendé d'azur" 7715), Troilus ("armes aveit a leonceaus | D'azur en or vermeil asis" 7756-7), Pyrrhus ("armes ot d'or a lionceaus" 23900), etc.
A 13th c. Florentine version (maybe a vernacular rendering of Guido delle Colonne's Historiae destructionis Troiae, which displaced Sainte-Maure's book in popularity) states that Hector bore a "scudo d' oro, ov' era uno leone azzurro" (Libro della distruzione di Troia, published by Alfredo Schiaffini in Testi fiorentini..., p. 173).
Excerpts of John Lydgate's early 15th c. adaptation into English, the Troy Book, are available here with an introduction. A 19th c. edition of Sainte-Maure is available in scanned format at Gallica (with a glossary).
Neubecker mentions that the Chapter of Mainz shows the arms of Christ (the charges are for the most part the instruments of the Passion). The Book of St. Alban's (1486) states: " Criste was a gentylman of his moder's behalue, and bare cotarmure of aunseturis." According to Morgan (1661), Adam bore plain Gules, and Eve bore plain Argent; logically, Abel had quarterly argent and gules. Joseph, recalling his coat, had chequy sable and argent. Each of Jacob's son has his own (the tribes of Israel did in fact have symbols, though I can only recall the lion of Judas).
And, of course, Dürer made a beautiful engraving of Death's coat of arms, shown in Neubecker next to God's coat of arms.