Who was the Greek king of Sparta in the Iliad?

The Greek king of Sparta in the Iliad was Menelaus, husband of Helen and brother of Agamemnon.

Menelaus leads the Spartan contingent in the Achaean army, although overall command belongs to his elder brother Agamemnon, king of Mycenae. The Trojan War begins because Helen leaves Sparta for Troy with Paris, the Trojan prince; Menelaus invokes the oath of Helen’s former suitors to bring the Greek forces against Troy.

In Iliad Book 3, Menelaus fights Paris in single combat, with Helen’s return as the prize. Menelaus gains the upper hand, but Aphrodite rescues Paris before the duel can settle the war. Later, Menelaus becomes one of the prominent Greek defenders of Patroclus’ body.

Readers often confuse Menelaus with Agamemnon because both are Greek kings and brothers. Agamemnon rules Mycenae and commands the expedition, while Menelaus rules Sparta and is the personal cause of the campaign. In the Odyssey, Menelaus and Helen are shown living again in Sparta after the war.