In Greek mythology, Ilus (Ilos) son of Tros founded the city called Ilios or Ilion (Ilium) — later Troy — following a dappled cow to the hill of Atë and receiving the heaven-fallen Palladium as Zeus' sign. Father of Laomedon, he preferred the new city to Dardania and left that realm to his brother Assaracus. He is distinct from the childless Ilus son of Dardanus and from minor Homeric/Virgilian namesakes.
Adapted from Wikipedia, "Ilus (son of Tros)" · CC BY-SA 4.0
I.Family
Ilus is son and heir of Tros of Dardania by Callirhoe (daughter of Scamander) or Acallaris; brother of Assaracus, Ganymede, and Cleopatra (and possibly Cleomestra). By Eurydice, Leucippe, or Batia he fathers Laomedon; daughters include Themiste and Telecleia. Some notices also give him Tithonus or even Ganymede as son — genealogies that conflict with the usual Tros → Ganymede line.
Homonym care: Apollodorus' earlier Ilus son of Dardanus dies childless (ilus-childless in this atlas); Odyssey hosts an Ilus son of Mermerus at Ephyra; Virgil names an Italian ally of Turnus. This entry is the founder of Ilium only.
II.Foundation and Palladium
Competing in Phrygian games, Ilus won a wrestling prize of fifty youths and maidens; an oracle bid the king add a dappled cow and tell him to found a city where she lay down — at the hill of Atë, where he built Ilium. Praying for a sign, he saw the Palladium fallen from heaven before his tent (three cubits high, spear and distaff in hand). Looking on it blinded him until he sacrificed to Athena; Dictys has it drop into Athena's unfinished temple through the open roof.
Grateful, he housed the image as Zeus' consent to the city's foundation.
III.Reign and tomb
Preferring Ilium to Dardania, he left the older kingdom to Assaracus on Tros' death, splitting the Trojan line. Later notices have him expel Tantalus from Paphlagonia and defeat Pelops, or beat Byzos of the Bebrykes. After his death the Trojans raised a great barrow before the gates — already a landmark in the Iliad's fighting.
Laomedon succeeded him on the throne of Troy.