Short answers, pulled from the story.
Memnon was a king of Aethiopia and a son of Tithonus, a mortal man, and Eos, goddess of the dawn. He fought on Troy's side during the Trojan War, carrying divine armor forged by Hephaestus, and was killed by Achilles.
Memnon was killed by Achilles in single combat. After Memnon slew Antilochus, the son of Nestor, Achilles fought him at Nestor's plea and drove his spear through Memnon's chest. Zeus used his golden scales to weigh their fates before the outcome was decided.
Zeus granted Memnon immortality after his mother Eos begged for mercy. Eos was permitted to see her son alive for a few moments each day when she opened the doors of heaven. The Aethiopians who buried Memnon were transformed into birds called Memnonides, which remained at his tomb.
The Aethiopis was an epic composed by Arctinus of Miletus, one of the cyclic poets, likely in the 7th century BC, after the Iliad. It focused on Memnon's death at Troy but survives only in fragments. Much of what is known about Memnon comes from later writers including Quintus of Smyrna's Posthomerica and Philostratus' Imagines.
The Colossi of Memnon are two stone statues of the Pharaoh Amenhotep III, approximately 3,400 years old, located in Luxor, Egypt. Greek and Roman visitors from at least the first century AD associated them with the mythical Memnon because the statues face the sunrise on the winter solstice.
After an earthquake in 27 BC, the northernmost colossus collapsed and began producing a musical sound at sunrise, which early Greek travelers interpreted as Memnon calling to his mother Eos. The Roman Emperor Hadrian and Empress Sabine visited to hear it in 130 AD. The sound ceased permanently after Septimius Severus ordered the statue restored, likely during his reign from 193 to 211 AD.