Greek Characters in the Comedy 
In the divine comedy, one finds characters from Greek Mythology spattered throughout.  He includes them as sinners, as they are pagan believers though they also serve the purpose of giving the audience familiar characters.  Dante was a student of the classics, and by including these characters he is able to entertain the audience while also driving home the essential themes of the comedy.

Ulysses- The hero of the Homeric epics the Iliad and the Odyssey, a warrior during the Trojan wars is found in the eighth pit of the Eighth, Fraudulent, Circle of Hell.  Ulysses is found with another Greek hero, Diomedes.  Ulysses is sent to Hell for coming up with the plan of the Trojan Horse, luring Achilles onto the island of Skyros, and stealing the Palladium- a statue of Athena that protected Troy.  Some think that Ulysses "Represents an immensely gifted individual not afraid to exceed established limits and chart new ground. It is perhaps appropriate that Dante prefaces the presentation of Ulysses with a self-reflective warning not to abuse his own talent." (Dante Worlds 8)

Achilles- We find Achilles, another Greek hero, in the Second, Lustful, Circle of Hell.  "Here Dante explores the relationship--as notoriously challenging in his time and place as in ours--between love and lust, between the ennobling power of attraction toward the beauty of a whole person and the destructive force of possessive sexual desire." (Dante Worlds 2) Again, the familiar character makes it easier for the readers to appreciate and understand why people are sent to this ring of hell.  Achilles is often regarded as one of the more sexual and beautiful Greek characters, and for many transgressions he is sent to this circle.