After Theseus had grown up, his mother advised him to roll away a large boulder. Under it, he found a sword and shoes. He then set out on his journey to Athens, where he would become heir to the throne. He chose a longer overland journey so that he could earn fame for his heroic deeds.

His first opportunity came just outside his native Troisena, when he encountered the lame giant Periphetes. Periphetes was a notorious robber who killed travellers with an iron club. But Theseus snatched the club from him and killed him. On the Isthmus, he met another robber named Sinnis, who in turn tied travellers to bent tree tops. When he then released the trees, the captives were torn apart. After a long struggle, Theseus overcame him and punished him with the same death.

Near Crommyon, Theseus killed the wild grey swine, Phaeaas (a descendant of Echinda and Typhon), who was destroying all the crops of the peasants. In the Megara region, another robber named Skeirón rampaged, throwing passers-by into the sea. But the hero was quicker, grabbed him by the legs and threw him into the depths. There was another robber named Kerkyon hiding around Eleusina. Those who passed by had to fight him in a life and death struggle. Theseus defeated and killed him.

The last robber on the road was Procrustes, who lured passers-by into his dwelling, where he had two beds. A short one and a long one. When someone lay down on the short bed, Procrustes cut off all the overhang. When he got on the long bed, he stretched him out the length of the bed. Théséseus threw Procrusteus on the short bed and cut off his head.

Thysseus entered Athens already with glory, but the local king Aigos (his father) did not immediately recognize him. Only Medea recognized him and tried to persuade Aiges to have Theseus murdered. She was unsuccessful, however, because the king eventually recognised his son by his sword and shoes. And then he banished Medea from Athens.

After a short time, the troops of Aigeus' brother Pallantus arrived at Athens, because Pallantus wanted to become the new king of the place. The defenders were led by Theseus, who destroyed the enemy with an unexpected blow, and Aigeos was able to remain king.

After this success, Theseus went on to other heroic deeds.

He killed a huge bull in Attica and then set out for Crete, which was being narrowed by Minotaur. Every ninth year, King Minos had to send seven maidens and seven young men into the labyrinth at the mercy of the terrible Minotaur. Minotaur was a monster with a human body and the head of a bull. He was the son of Minous' wife, Pasiphae, who was unfaithful to her husband with a white bull.

Theseus decided to enlist in a select sacrificial group so that he could kill the monster. Importantly, Minous' daughter Ariadne fell in love with him and gave him a magic sword and a ball of thread. The hero left the group near the entrance and went into the labyrinth alone, ball of thread in hand. In the centre of the labyrinth he fought a battle with a monster, which he managed to defeat. He then found Ariadne and fled the island with her. Together they reached the island of Naxos, from which only Theseus sailed the next day. There are two different versions of the story at this point, namely that Théseus simply forgot about Ariadne, or that the god Dionysos commanded her to stay in a dream (he wanted to marry her). When Theseus sailed to Athens, he made a terrible mistake. He had forgotten to change his black sail for a white one (for he had agreed with his father before the voyage that when the ship returned home, the black sails would mean Théseus' death, the white ones life and victory). So his father Aigeus jumped into the sea in great grief and died. Théseus thus became the new king.

Together with Iason, Thésus then sailed on the Argonauts' ship to the distant Colchis for the golden fleece. He again fought alongside Heracles against the Amazons. He returned home with their leader, Antiope, who became Théseus' wife. The Amazons then tried to rescue her, but Antiope sided with Theseus and was killed in an attack on Athens.

In time, Theseus began to lust after the beautiful Helen of Sparta, the cause of the future Trojan War. Peirithoos also coveted her, but through the luck of the draw, Helen fell to Theseus. Peirithoos then sought out Persephone, wife of the god of the underworld, Hades. He and Théséos set out for her, but could not convince her to leave. Hades then imprisoned them both. After a long time, Thésus was freed by Heracles. In the meantime, Helen was kidnapped by her brothers and Menestheos, who was Théseus' arch-enemy, took control of the city. The hero became a mere outlaw.

Théseus died on the island of Euboia, where he sought his sons in order to recapture Athens. He was killed by the Skyrian king Lycomedes, who coveted his possessions. His death was brought about by a fall into the sea.