A lazy question as I should check, but- there is a chronology of sorts for Greek mythology, due largely to its genealogies. (Theseus, for example, is nearly killed by his father Aegus’s wife, Medea, whose marriage to Aegus came after her marriage to Jason, and since Jason left Medea to marry the daughter of Creon who was already king in place of his nephew Oedipus, etc., it establishes something of a chronology.
So is there a hero who is the starting point of Greek legends? (I’m familiar with the myths of the birth of Zeus & Co., but I’m referring to the heroes as opposed to the gods and demigods.)