Konstantin Kastrioti Mazreku is attested in Giovanni Andrea Angelo Flavio Comneno's Genealogia diversarum principum familiarum.

Angelo used the cognomen Meserechus in reference to Skanderbeg, and this link to the same name is produced in other sources and reproduced in later ones like Du Cange's Historia Byzantina (1680).

Angelo calls Gjon Kastrioti's father "Georgius Castriotus" (Gjergj), lord (princeps) of "Aemathiae, Umenestria" (Mat and probably Ujëmisht) and "Castoriae".

This is considered a very unlikely trajectory in the context of Albanian medieval society because noble families had acquired their area of influence over multiple generations in a complex system of affiliation with local village communities and intermarriage with each other.

[8] Historian Kristo Frashëri considers it likely that he ruled over his region "in the third quartier of the 14th century" between 1350–75, based on the fact that when his grandson Gjergj Kastrioti was born, his son Gjon had already fathered seven children with Voisava, daughter of a minor lord from the Polog Valley.

[10] Gjon Kastrioti rose as a feudal ruler in Albania at a time when its internal politics were being increasingly dominated by the Republic of Venice, which controlled many of its trade centers, and the Ottoman Empire, which in one form or another had begun to vassalize many of the small, independent lordships.

In 1402, Kastrioti, Koia Zaharia, Dhimitër Jonima, and other Albanian vassals of Ottoman Sultan Bayezid I personally led their retinues in the Battle of Ankara.

In the power vacuum that formed, Kastrioti strengthened his position and sought to expand towards the coastal areas near the Venetian-controlled trading centers.

Lazarević had taken Zeta from Balša III in 1421, but the Venetians did not recognize him, holding on to the occupied Zetan coast and Buna, including Drivast.

[15] In August 1421, Lazarević led armies into Zeta and took Sveti Srdj, Drisht, and Bar; the Venetians concluded a truce and now held only the towns of Shkodër, Ulcinj, and Budva.

[19] In January 1423, Venice bribed and won over the Pamaliots on Bojana and then bought over several tribal leaders in or near Zeta: the Paštrovići, Gjon Kastrioti (who had extended to the outskirts of Lezhë), the Dukagjins, and Koja Zaharia.

In 1428, Gjon Kastrioti had to seek forgiveness from the Venetian Senate because of Skanderbeg's participation in Ottoman military campaigns against the Christians.

[30] Collecting the custom duties from Ragusan traders, exporting the grain, and trading with salt were important sources of income for Gjon Kastrioti.

[32] With that letter, Gjon informed merchants from Dubrovnik that they were granted safe conduct when passing through regions under his control on their way from Shufada to Prizren.

At the beginning of the 15th century, Šufaday (an important former marketplace on the Adriatic Sea, near Lezhë) was a possession of the Jonima family, and in 1428 it was under Gjon's control.

[38] In 1426, he donated the right to the proceeds from taxes collected from the two villages (Rostuša and Trebište in North Macedonia) and from the church of Saint Mary, which was in one of them, to the Serbian Orthodox monastery of Hilandar in Mount Athos, where his son Reposh retired and died on 25 July 1431.

[52][53] Besides the acts in Slavonic, Ivan is used by some Byzantine chroniclers, like Laonicus Chalcocondyles (Ὶβάνης)[54] and many works written by the contemporary scholars.

Frang Bardhi (1606–1643) in his Apology, dwelling on an Albanian named Gjon Kastrati, states that: "Gion, which in Latin is Iohannis".

)La note en question, datée 1438, ne laisse subsister aucun doute que c'est autour de cette date que ces terres avaient été cadastrées.