He had many other adventures, he was one of the Argonauts for example. He saved the life of his friend, Pirithous, a number of times. Pirithous liked danger as well as Theseus but he wasn´t as successful as him as he was always in trouble. He wanted to see if Theseus was as great a hero as he was to be and he stole some of Theseus´ cattle. When he heard that Theseus found out, instead of running, he decided to face Theseus. But as the two of them faced each other, Pirithous held out his hand and apologized to Theseus. Apology was accepted and their friendship went on without harm.

When Pirithous was getting married, Theseus was there as a guest and he was very useful there. The centaurs were related to the bride and they came to the wedding. They got drunk and one of them tried to carry her away. Theseus saved her and terrible fight followed. They managed to get rid of the centaurs with Theseus´ help.
After the disastrous wedding, Pirithous decided that he wanted the most carefully guarded lady in all the universe for his second wife, Persephone herself. Theseus agreed to help him but first he kidnapped Helen, then a child – he wanted to marry her when she grows. Helen´s brothers got her back, fortunately for Theseus, he was already on his way to get Persephone.

They came to the underworld and Hades, perfectly aware of why they came, invited them to sit in his presence. They considered it friendly gesture and they sat on the seat he wanted them to and they stayed there, as it was the Chair of Forgetfulness. If someone sat on it, they forgot everything and could not move. Hercules saved Theseus, but he didn´t manage to save Pirithous too, because Hades knew that it was his plan to carry Persephone away.
Later, Theseus married Ariadne´s sister Phaedra and that brought terrible misfortune on her, him and his son Hippolytus. He had sent Hippolytus away as a child to the same town he had spent his youth. His son turned to the great man, but he scorned Aphrodite, he worshipped only Artemis. When Theseus came to see him, bringing Phaedra with him, he didn´t even noticed her, he enjoyed company of his father. Phaedra, on the other hand, fell in love with him. Aphrodite, who has angry with Hippolytus, decided to punish him.

Phaedra desperate of love, decided to kill herself and let no one know why. Theseus was out of town but her old nurse, who really loved Phaedra, discovered everything. She went straight to Hippolytus and told him about Phaedra´s determination to die and about her love for him. He, however, wasn´t interested in women at all and especially this love sickened and horrified him. He was angry at the old woman and left.

Phaedra, hearing that, killed herself and left a letter for her husband. When he came home and found her dead, he opened the letter and read it again and again. He cursed his son, as in letter was that „his son laid his violent hands upon his wife“. He also banished him from land although Hippolytus tried to defend himself, he didnt believe him. Hippolytus went, but not into exile, his father´s curse came true and he had an accident. Artemis appeared to Theseus and told him the truth. Hippolytus, still not dead was carried in. He forgave his father and died. Artemis let Theseus know that Aphrodite killed his son, not him.
Theseus was at court of a friend, king Lycomedes and he killed him, no one knows why. The Athenians honored Theseus as a great hero, as they did with no other mortal.