In my series, the title given to the bull-god, the sacred king. He was, as far as I can tell, the precursor to Zeus, although later myths say he was the son of Zeus.
Carl Kerényi has a whole chapter on Zagreus in Dionysos, Archetypal Image of Indestructible Life, which of course I won’t repeat in its entirety here. The highlights:
page 113: “The Cretans of the Greek period spoke of a Zeus of their own, stressing the Cretan mythologem of his birth by the use of the epithet “Kretogenes,” “he who was born in Crete.” By this they meant the god born in a Cretan setting that included the cave. If we drop the Greek names “Zeus” and “Dionysos,” there remains the great anonymous snake god who, according to the late testimony of Himerios, held his marriage “in Cretan caves.”
“Less archaic than the seduction by a snake was the universally known myth of the rape of Persephone. “Hades,” “Plouton,” or the “subterranean Zeus” were only cover names for the ravisher. Fundamentally he too was a great anonymous god. To the version in which the scene of the rape was Sicily, Nonnos in his Dionysiaka appended an account of the snake marriage. Demeter leaves Crete with her virgin daughter Persephone and hides her in a cave near the spring of Kyane. Thither comes Zeus, the bridegroom in the form of a snake:
…through marriage with this heavenly dragon
Persephone’s womb became fruitful, prepared
To give birth to Zagreus, the horned infant.
Aischylos bears witness to the contradictory identity of Zagreus, on the one hand with a “subterranean Zeus,” on the other with his subterranean son. “Zagreus,” “he who captures alive,” was also a cover name, a circumlocution for a great god, in fact the greatest god of all time. He visits his hidden daughter in a cave, and she bears him to himself as his own son. The “mystic” feature which we have presupposed in the relationship between Dionysos and Ariadne here appears in an archaic myth in which generation and birth never go beyond the same couple. Taking his mother or daughter to wife, the son or husband begets a mystic child who in turn will court only his mother. To such involvements the snake figure is more appropriate than any other. It is the most naked form of zoë absolutely reduced to itself”
Later in the book, Carl observes: “It is certain that if Pentheus, a transparent and unequivocal name with the somber meaning “man of suffering,” could become a man’s name at Knossos it was only because the names of gods–“Zagreus” as well as “Pentheus”–were also given to persons and because int he fesstive calendar the god’s somber aspect prepared the way for the opposite aspect.”
Robert Graves says on page 110 in The Greek Myths:
“Because the vine cult reached Greece and the Aegean by way of Crete–oinos, ‘wine’, is a Cretan word–Dionysus has been confused with Cretan Zagreus, who was similarly torn to pieces at birth.”