Tros belongs to the oldest Trojan genealogy. Homer gives the essential line in the speech of Aeneas to Achilles. Zeus begat Dardanus, who founded Dardania on the slopes of many-fountained Ida before the city of Ilium existed in the plain. Dardanus begat Erichthonius, who became the richest of mortal men because his meadows contained three thousand mares with their foals. Erichthonius begat Tros, and Tros in turn had three peerless sons: Ilus, Assaracus and Ganymede. Ilus founded the line of Laomedon and Priam; Assaracus founded the line that led through Capys and Anchises to Aeneas himself. Homer's genealogy therefore makes Tros the dividing point between the old Dardanian house and the twin lines of Troy and Dardania.

Apollodorus expands the family. Dardanus had two sons, Ilus and Erichthonius. The elder Ilus died childless, so Erichthonius inherited the kingdom. He married Astyoche, daughter of the river Simoeis, and she bore Tros. When Tros came to the throne, he renamed the land Troy after himself. He married Callirrhoe, daughter of the river Scamander, and she bore a daughter Cleopatra and three sons: Ilus, Assaracus and Ganymede. The names matter because Homer places the Trojan kings within a landscape defined by rivers, mountains and pastures. Simoeis and Scamander water the plain; Ida rises above the city; the horses of Erichthonius and Tros symbolise the wealth of the Trojan royal house.

Dionysius of Halicarnassus gives a different marital and maternal tradition. He names Erichthonius' wife as Callirrhoe, daughter of Scamander, and Tros' wife as Acallaris, daughter of Eumedes. In this version Tros fathers Assaracus but does not enumerate the full family in the same way. The variation shows that Roman and Greek genealogists adjusted the Trojan house to fit their own traditions. Yet the central line remained stable: Dardanus, Erichthonius, Tros, Ilus and Assaracus, with Ganymede as the divine interruption.

Tros' father Erichthonius was famous for horses. Homer says he possessed three thousand mares, and the North Wind Boreas, seeing them graze, took the form of a dark-maned stallion and covered them. They bore twelve fillies that could run across the tops of ripe grain without breaking the ears and over the surface of the sea without sinking beneath the waves. When Erichthonius passed the kingdom to Tros, the horses passed into the mythology of Troy. The dynasty's power rested not only on land and walls but on swiftness, breeding and divine favour.

Tros inherited that wealth and rule. The Iliad says he became king among the Trojans, while Apollodorus explicitly states that the country was called Troy after him. Strictly speaking, the city of Ilium was founded by his son Ilus and originally bore that son's name. The land and people, however, bore the name of Tros. Later writers simplified the distinction and made Tros the founder of Troy in a broader sense. He is therefore an eponym before he is a builder: a king whose name turns a Dardanian population into Trojans.

Ilus continues the branch associated with the city of Ilium. A later foundation tradition says Ilus wins a contest in Phrygia, follows a cow until it lies down and establishes the city at that spot. This story is not narrated by Homer and should not be attributed directly to Pseudo-Apollodorus without qualification. The important distinction is that Tros gives his name to the Trojans and the country, while Ilus is the figure later credited with founding Ilium.

Assaracus remained king of the older Dardanian territory. He married Hieromneme, daughter of Simoeis, and fathered Capys. Capys married Themiste, daughter of Ilus, joining the two branches of Tros's family. Their son Anchises lay with Aphrodite and fathered Aeneas. Aeneas became the leading Dardanian warrior of the Trojan War and the man destined to survive the city's fall. The Roman tradition traced its ancestry through this line, making Tros an ancestor not only of Priam and Hector but also of Aeneas, Ascanius, Silvius and the Roman people.

The third son, Ganymede, interrupted the dynastic pattern. Homer calls him godlike and the fairest of mortal men. The gods caught him up to be Zeus' cupbearer because of his beauty, so that he might dwell among the immortals. Later versions make Zeus carry him off in the form of an eagle or send an eagle as the agent of the abduction. Tros, who did not know what had happened to his son, grieved as though Ganymede had died. Zeus sent Hermes to explain that the boy was immortal, would not age and would hold the honoured place of cupbearer among the gods. Some traditions add that Tros received a gift of horses or a golden vine as compensation for his loss.

The immortal horses became part of the Iliad's war narrative. In Book Five, Aeneas tells his ally Pandarus that the horses he drives descend from the stock Zeus gave to Tros as recompense for Ganymede. Anchises later stole a breed from Laomedon's mares while the king did not know, and from that theft six foals were born. Anchises kept four and gave two to Aeneas. Those horses become visible proof of Tros' family wealth reaching across generations to the battle before Troy. Even when Tros himself has vanished from the action, his horses remain active in his descendants' war.

The story of Ganymede also gives Tros a rare emotional presence. Most Greek genealogies are lists of names, marriages and successions. Tros, however, experiences loss. The gods take his son from the earth, and he grieves until Hermes explains the abduction. His grief makes the divine transaction human. Zeus gains a beautiful cupbearer, Olympus gains a youth who will never age and Tros loses the child who would have stood beside him in Dardania. The gift of horses converts the loss into honour, but it cannot restore the son.

Tros receives no developed battles, speeches or death scene in the surviving traditions. Homer does not narrate his reign beyond genealogy. Apollodorus treats him as a bridge between Erichthonius and the founding of Ilium. Dionysius uses him to prove the Greek or at least properly ancient origins of the Trojan race. Dictys Cretensis preserves him in the same genealogical pattern. His role is structural rather than dramatic. He links Dardanus to Ilus, the Trojan War and the Roman foundation myth.

That structural role is nevertheless immense. Greek myth gives the Trojan people not one founder but a succession of namers. Dardanus gives his name to Dardania. Tros gives his name to Trojans and the Troad. Ilus gives his name to Ilium. The layering reflects Greek memory of different populations and settlements in the Troad. A city can change name while a people preserve an older identity. Tros marks the point where the Dardanian dynasty becomes recognisably Trojan.

His family tree also contains the central tension of Trojan myth. The line of Ilus produces the city of walls, pride and war. The line of Assaracus produces Aeneas, the man who carries Troy beyond destruction. In Homer, Aeneas addresses Achilles and traces both lines back to Tros. His genealogy is a claim to legitimacy. He is not merely a cousin of Priam. He descends from the same Tros who gave the Trojan people their name and from the same horse-breeding house that supplied the divine chariot team he drives into battle.

Roman writers intensified that legitimacy. Virgil, Dionysius of Halicarnassus and later imperial genealogists needed Aeneas to be both Trojan and worthy of founding Rome. Tros gave them the bridge. Through Tros, Aeneas descended from Zeus via Dardanus, from the wealth of Erichthonius and from the stock of Ganymede's immortal horses. Through Assaracus, he belonged to the older Dardanian line that survived even when Ilium fell. The city of Troy could burn, but the name of Tros would survive in Italy.

Ancient art rarely isolated Tros as a principal figure. Greek vase painters preferred Ganymede's abduction, the later stories of Troy and the battles of the Trojan War. Roman genealogical reliefs, wall paintings and coins used the Trojan ancestors as a chain of names and images. Tros appears more often in text than in art, remembered as a father, eponym and horse king rather than as a hero with a single defining deed.

Modern retellings often omit him or reduce him to one line in the Trojan family tree. Yet the name he carries explains why Troy is Troy. Dardanus founded the house. Erichthonius created its fabulous wealth. Ilus built the city. Priam ruled it during its destruction. Aeneas carried its people toward Rome. Tros stands behind them all, the king whose name gave the land and people their collective identity.

The accurate record of his life is therefore genealogical rather than biographical. He was the son of Erichthonius and Astyoche, or in some traditions of Callirrhoe. He married Callirrhoe or Acallaris. He fathered Cleopatra or Cleomestra, Ilus, Assaracus and Ganymede. He became king of Dardania, gave his name to the Trojans and the Troad, and inherited the divine horse stock of his father. When Ganymede was taken to Olympus, Tros grieved and received immortal horses as recompense. His sons divided his kingdom into the lines of Troy and Dardania. His death is not recorded. His memory survives in the name of every Trojan who fought beneath the walls of Ilium.