%magnum opus%

n. 1. A great work of art or literature. [ WordNet 1.5 ]

2. The greatest work or achievement of a particular artist, writer, or other individual. [ PJC ]

Inspired by this milieu, [ Max Stirner ] wrote his magnum opus The Ego and Its Own, which was published in November 1844. Svein Nyberg (The Small Max Stirner Web Page, 1988 [ https://web.archive.org/web/19981207014247/http://www.math.uio.no/~solan/stirner/stirner.html ]) [ PJC ]