Epicurus
Epicurus was born in the year 342 BCE on the island of Samos, though an Athenian by right. He founded his school in Athens c. 304, where he purchased a garden in which he lived with his disciples and delivered his lectures, and in which he stayed for the rest of his life. He died from a stone in the bladder in 270 BCE, at the age of 72, and had then been settled in Athens as a teacher for thirty-six years.
Physics
Epicurus essentially followed the doctrines Democritus, who taught that the universe consists of two elements, matter (soma) and space, or vacuum (to kenon), in which matter exists and moves; and all matter is reducible to indivisible particles or atoms (atomoi), which are eternal. These atoms are in constant motion; their natural motion is straight downward, but occasionally they swerve inexplicably, causing collisions. It is the chance collisions and subsequent joining together of these atoms of various shapes and sizes that brings about the universe as we see it.
The gods exist, but are themselves only finer and longer-lasting creations of blind chance; they did not create the world, and are not troubled much about it; rather, they live a life of serene calm (the highest pleasure) in remote ease.
The soul does in fact exist, but it is a material substance that dissipates at the moment of death.
Ethics
Pleasure is the highest good, but for Epicurus, the things that are normally thought to be pleasurable -- food, sex, drinking, etc. -- are in fact quite painful, as they cause severe disturbances in the body and soul. For Epicurus, the highest pleasure is being in a state of absolute lack of pain -- ataraxia -- and he and his followers sought this state by frugal living, eating only barley cakes and water, and abstaining as much as possible from public life and from sensual disturbances. Epicurus himself remained a bachelor, and advised his followers to abstain from marriage and sex if they were able.The highest intellectual pleasure is the serene contemplation of the nature of things -- as we shall see in Lucretius.
Religion for Epicurus was a great evil, instilling needless fear of death and a superstitious fear of vengeful and capricious gods. This sentiment is wonderfully summed up in one of Lucretius' more memorable lines, when he says, after recounting a human sacrifice, tantum religio potuit suadere malorum ("so much evil could religion inspire").