Acher (Heb.). The Talmudic name of the Apostle Paul. The Talmud narrates the story of the four Tanaim, who entered the Garden of Delight, i.e., came to he initiated; Ben Asai, who looked and lost his sight; Ben Zoma, who looked and lost his reason; Acher, who made depredations in the garden and failed; and Rabbi Akiba, who alone succeeded. The Kabalists say that Acher is Paul.
Source: H.P.Blavatsky - The Theosophical Glossary