St. Isidore was a rich Alexandrian who made the "mistake" to be a Christian during the reign of emperor Decius, the most notorious prosecutor of Christianity.  He arrived in Chios in 250 CE as a military officer.  With his house adjacent to brothels, he made the acquaintance of working girls, 2 of whom he converted to Christianity. 

The General Numerianus ordered Isidore arrested, and demanded he repent.  When Isidore refused, he was condemned by death by fire.  He was put into a furnace, and when he did not burn, he was tied to a horse and dragged through the countryside of southern Chios.  As was usual with Christian martyrs, he was also beheaded to thwart the possibility of resurrection.

Years later, when Christianity prevailed, the Chians linked their mastiha to the new religion by way of their St Isidore, proclaiming that the skinos trees before which the saint was martyred, miraculously wept and that the mastiha was their tears.  Smart marketing on the Chians part---they essentially increased the value of mastiha by making deeming it holy, and gained access to the lucrative incense market in the Christian churches. 

The 17th century Chian scholar Leon Allatius, recognizing that the "miracle" of Isidore did not hold water, modified the original legend.  He admitted mastiha existed before Isidore's time, but added that it acquired its distinctive aroma only after the skinos trees witnessed his martyrdom. 

See our Kleos founder, Effie Panagopoulos, recount the story of St. Isidore, as told to her by the Chian locals, below: 

Or get it right from the horse's mouth from Evgenia Almiroudi, Mesta farmer below:  (greek with subititles)