The Mortal Immortal

The story begins on July 16, 1833, the apparent three hundred and twenty-third birthday of the narrator, Winzy, the self-styled "mortal immortal". Winzy recounts the series of events that lead him to drink an "elixir vitae" at age twenty, during his employment under alchemist Cornelius Agrippa. Winzy was offered gold to stay under Agrippa's tutelage after one of Agrippa's former assistants had "raised [a] foul fiend during his master's absence, and was destroyed by him".
Winzy is terrified, but accepts ... (courtesy of mary-shelley-wikia.com)