Final answer:
Heracles is considered Zeus's favorite son due to his half-divine origin, his completion of the Twelve Labors, and his representation as a figure of might and virtue, which aligned with Zeus's own pre-eminent position and characteristics as celebrated in the Orphic Theogony.
Step-by-step explanation:
Heracles, known as Hercules in Roman mythology, is often considered Zeus's favorite son because of his demi-god status and the courageous feats he accomplished. According to the myth, Zeus, who is consistently described as having a 'roving eye' and fathering children with various human maidens, secretly placed his infant son Heracles at the breast of Hera to imbue him with immortality. The act itself demonstrates Zeus's affection by seeking divine powers for his son. Moreover, Heracles's successful completion of the Twelve Labors, including slaying the Nemean Lion and obtaining the apples of the Hesperides, further solidified his position as a favored son of Zeus, celebrated in both art and legend.
In addition, the Orphic Theogony emphasizes Zeus's supreme position as the creator and central force of the cosmos, from which all things are fashioned, shining a light on the rationale behind Zeus's pride in Heracles, his son, who demonstrated both might and heroic virtue.