Dante's guide is the poet Virgil, a Roman poet that would have been well-known in Dante's era.
Dante visits Ulyssess/Odysseus in his travels. In his encounter, reference is made to the Trojan War and to other fighters in that war - Achilles, Agammenon, Diomede, etc. Canto XXVI
He also encounters Brutus and Cassius, some of the men responsible for the death of Julius Caesar of Rome. Canto XXXIV.
Judas Iscariot, the betrayer of Jesus, is in Canto XXXIV.
Dante uses these historic names, as well as characters from many myths, because they would be familiar to the readers of his time and provide better examples of the sins he was trying to describe.