magnum opus

noun3

1. •
   A great or important work of literature, music or art, a masterpiece.
2. •
   The best, most popular, or most renowned achievement of an author or artist, representing their major life effort.

   • The 1949 novel Nineteen Eighty-Four is widely considered to be George Orwell's magnum opus.
3. •
   The process of working with the prima materia to create the philosopher's stone.