(Canto 10, line 14)
Epicurus (341-270 BC) was an ancient Greek materialist philosopher, the founder of a famous philosophical academy in Athens (306 BC). He was an adherent of the atomist teachings, which held that the universe was composed of atoms. The life and death of living creatures were therefore also determined by the joining and disjoining of atoms: according to this theory, even the soul was composed of even smaller particles, which disintegrated after a persons death - the soul does therefore not possess immortality. He did not deny the existence of gods, but held that gods existed only in an extremely distant dimension and never interfered in the affairs of men: therefore, man need not fear death (which is only a "long sleep"). While alive on earth, he believed that people should seek to distance themselves from suffering and attain a state of mental peace he termed "ataraxia", which is also very different from an uninhibited pursuit of pleasure. He believed that the motivation for action was ultimately to be found in the human spirit and not simply in material "pleasures". Dante probably learned of Epicurus' teachings through the writings of Cicero. In his Convivio, he neutrally characterises Epicurus' teachings by saying that living things are instinctively "avoiding pain and seeking pleasure, said that this end of ours was pleasure - that is, delight free from pain".
In fact, since Epicurus' teachings existed before the birth of the Christ, they should theoretically not be considered heretical, but during the Middle Ages, all theories denying the immortality of the soul were automatically considered such, and "epicurean" was even used as a term for such a belief. Dante, in this very much a product of his times, in another passage of the Convivio accordingly condemnds such denial as "of all the follies the most foolish, the basest, and the most pernicious". In Dante's times, the epithet of "epicurean" was sometimes even extended to the Ghibelline party for their opposition to the Pope wielding secular power. The medieval Inquisition would normally sentence heretics to be burned at the stake - maybe in accord with this must their souls in circle 6 also suffer a similar punishment.
Based on these two Convivio passages, some scholars believe that Dante's opinions on Epicurus underwent a certain change over time: on the other hand, they clearly adress different questions and should maybe not be taken as a clear indication that such is the case.