Mythology & Beliefs: Leda In Greek and Roman Mythology, Leda was the mortal loved by Zeus in form of
swan; mother of Helen, Clytemnestra, Dioscuri.
Leda in Greek and Roman Biography and Mythology
（*Lh/da), a daughter of Thestius, whence she is called
Thestias (Apollod. 3.10.5; Paus. 3.13.8; Eur. IA 49); but
others call her a daughter of Thespius, Thyestes, or
Glaucus, by Laophonte, Deidamia, Leucippe, Eurythemis, or
Paneidyia. (Schol. ad Apollon. Rhod. 1.146, 201 ; Serv. ad
Aen. 8.130; Hygin, Fab. 14; Apollod. 1.7.10.) She was the
wife of Tyndareus, by whom she became the mother of
Timandra, Clytaemnestra, and Philonoe. (Apollod. 3.10.6;
Hom. Od. 24.199.) One night she was embraced both by her
husband and by Zeus, and by the former she became the mother
of Castor and Clytaemnestra, and by the latter of Polydeuces
and Helena. (Hyg. Fab. 77.) According to Homer (Hom. Od.
11.298, &c.) both Castor and Polydeuces were sons of
Tyndareus and Leda, while Helena is described as a daughter
of Zeus. (Il. 3.426; comp. Ov. Fast. 1.706; Hor. Carm. 1.12,
25; Martial, 1.37.) Other traditions reverse the story,
making Castor and Polydeuces the sons of Zeus, and Helena
the daughter of Tyndareus. (Eur. Hel. 254, 1497, 1680;
Schol. ad Apollon. Rhod. 2.808 ; Hdt. 2.112.) According to
the common legend Zeus visited Leda in the disguise of a
swan, and she produced two eggs, from the one of which
issued Helena, and from the other Castor and Polydeuces.
(Schol. ad Eurip. Orest. 453; Ov. Her. 17.55 ; Paus. 3.16.1;
Horat. Ars Poet. 147; Athen. 2.57, &c., ix. p. 373; Lucian,
Dial. Deor. 2.2, 24.2, xxvi.; comp. Virgil, Cir. 489; Tzetz.
ad Lycoph. 88.) The visit of Zeus to Leda in the form of a
swan was frequently represented by ancient artists. It
should be observed that Phoebe is also mentioned as a
daughter of Tyndareus and Leda (Eur. IA 50), and that,
according to Lactantius (1.21.), Leda was after her death
raised to the rank of a divinity, under the name of Nemesis.
(Comp. TYNDAREUS.) - A Dictionary of Greek and Roman
biography and mythology, William Smith, Ed.
Leda in Wikipedia
In Greek mythology, Leda (Λήδα) was daughter of the Aetolian
king Thestius, and wife of the king Tyndareus (Τυνδάρεως),
of Sparta. Her myth gave rise to the popular motif in
Renaissance and later art of Leda and the Swan. She was the
mother of Helen (Ἑλένη) of Troy, Clytemnestra
(Κλυταιμνήστρα), and Castor and Pollux (Κάστωρ & Πολυδεύκης,
spelled Kastor and Polydeuces).
Leda was admired by Zeus, who seduced her in the guise of a
swan. As a swan, Zeus fell into her arms for protection from
a pursuing eagle. Their consummation, on the same night as
Leda lay with her husband Tyndareus, resulted in two eggs
from which hatched Helen — later known as the beautiful
"Helen of Troy" — Clytemnestra, and Castor and Pollux (also
known as the Dioscuri (Διόσκουροι). Which children are the
progeny of Tyndareus, the mortal king, and which are of
Zeus, and are thus half-immortal, is not consistent among
accounts, nor is which child hatched from which egg. The
split is almost always half mortal, half divine, although
the pairings do not always reflect the children's heritage
pairings. Castor and Polydeuces are sometimes both mortal,
sometimes both divine. One consistent point is that if only
one of them is immortal, it is Polydeuces...