In Greek mythology, Achilles was a great warrior and the hero of the Trojan War. He was the central character of Homer's Iliad.

Achilles was nearly invulnerable because his mother dipped him in the River Styx as an infant. She held him by the heel when she did so, and so he developed a weak point on his heel.

He was most famous for slaying Hector outside the gates of Troy. Later, he was shot in the heel by Paris.

Achilles had a close friendship with Patroclus. Every version of the story features their intimate friendship, but many interpretations also present them as lovers. In Plato's Symposium, participants in a dialogue assume that Achilles and Patroclus were romantically involved. When Achilles learns of Patroclus's death during the Trojan War, he is deeply grieved, laments loudly, and smears himself with ash. After the death of Achilles, the bones of the two men were mingled. 

Wikimedia/The Rage of Achilles, fresco by Giovanni Battista Tiepolo

In addition to his close relationship with Patroclus, Achilles had Briseis. In various retellings, she is a slave, a concubine, or a wife. Agamemnon takes Briseis from Achilles, which causes Achilles to leave the war. He only returns after the death of Patroclus and when Briseis is returned to him. On her return, Agamemnon swears to Achilles that he never slept with Briseis. 

She remains with him until Achilles's death and grieves deeply when she learns about it. Briseis is the one who prepares Achilles for the afterlife.

An old Greek painting with thin lines and details.
Wikimedia/Achilles tending Patroclus wounded by an arrow