Osiris was the Egyptian god of the underworld, as well as a fertility and agricultural deity. With his wife, Isis, he was the father of Horus. Beb was described as his first-born son. Later, he was combined with Seker and Ptah to create Ptah-Seker-Osiris and was also identified with Heryshaf.
(for the long version of the following story, see Legend of Osiris and Isis)
Osiris was murdered by his brother, Seth, who then chopped the body into smaller pieces. Isis and Nepthys, her sister, found the pieces (except his penis) and gave wax models of them to the priests to worship. Re sent Anubis and Thoth to mummify Osiris and Isis brought life back into his body. Afterwards, Osiris had to stay in the underworld and judge the souls of the dead and was called Neb-er-tcher ("lord of the outermost limit").
The Egyptian Ministry of Tourism website says that Orisis "once possessed human form and lived upon earth, and that by means of some unusual power or powers he was able to bestow upon himself after the death a new life which he lived in a region over which he ruled as king, and into which he was believed to be willing to admit all such as had lived a good and correct life upon earth".
The hieroglypic rendering of this God's name is still uncertain. Current thinking is that it is pronounced "aser" where the "a" is a glottal stop much as you still hear in modern the Arabic and Hebrew languages.
Some information used in this article came from the Egyptian Ministry of Tourism's website at http://touregypt.net/osiris.htm