(here designated Isaac IV) The Angeli claimed to be direct male-line descendants of Emperor
Isaac II Angelos (), and thus a branch of the
namesake Byzantine Greek dynasty. They also claimed that Isaac II was a direct descendant from
Constantine the Great ().
Giovanni Andrea I Angeli (1569–1634) claimed Isaac II was his ancestor in the ninth degree. Although Isaac II had many descendants in the female line, being related to many noble and royal houses in Europe through his daughter
Irene Angelina, and had sons, all documented direct male-line descendants were long dead before the Angeli arrived in Italy. The male line of the Angelos emperors is not recorded to have survived beyond the death of Emperor
Alexios III Angelos in 1211. Later members of the Angelos family descended from
John Doukas, uncle of Isaac II and Angelos III. John's descendants, who often preferred to use the name 'Komnenos Doukas' rather than 'Angelos', ruled
Epirus and
Thessaly until the 14th century. Among their last known recorded descendants were
Michael Angelović (), a Serbian magnate, and
Mahmud Pasha Angelović (1420–1474), who served as the
grand vizier of the
Ottoman Empire under Sultan
Mehmed II, in 1456–1466 and 1472–1474. It is possible that the later Angeli in Italy either directly or collaterally descended from less well known children or cousins of the Angelos emperors. That there might be some truth to the Angeli's claim to illustrious descent is strengthened by the willingness of other Balkan nobles, in part of actual royal lineages, to accept their descent. Descent through female lines, claimed by some of the members of the family, is also plausible. The claims of the Angeli of imperial descent were accepted in Western Europe without much dispute: there were already several known descendants of Byzantine nobility across the continent, legitimate or not, so the addition of another family was not surprising. The earliest certain ancestor of the Angeli was the Albanian noble Andres Engjëlli (Hellenized as "Andreas Angelos" and written as "Andrea Angelo" in Italian), attested in the 1480s. Andres Engjëlli married Dorothea Arianiti of the prominent
Arianiti family. The eldest son of Andres Engjëlli,
Pal Engjëlli (later called Paolo Angeli in Italian sources), was a counsellor and supporter of
Skanderbeg, who led Albanian resistance against the Ottomans. Pal's younger brother Pjetër (later called Pietro in Italian sources) married Lucia Span, the daughter of
Peter Spani, one of the most prominent Christian leaders in Albania. Once the Albanian resistance against the Ottoman Empire was defeated and the country was conquered, the Angeli escaped to Italy. In 1545, the brothers
Andrea and Paolo Angeli, sons of Pjetër, were officially acknowledged as descendants of the Angelos emperors by Pope
Paul III (). The two brothers were also guaranteed the right to inherit territory in the former Byzantine Empire, should such territory be recovered from the Ottomans, and, as recognized heirs to the Byzantine imperial title, given the right to appoint princes and even kings themselves. The papacy was eager to support the Angeli, not only because Pope Paul III had genuinely believed their claims, but also because a family of Catholic descendants of Byzantine emperors provided hope that if the Ottomans were ever driven out of the Balkans, the Byzantine Empire could be restored under a Catholic dynasty, religiously obedient to the papacy. == Foundation of the Constantinian Order ==