Medicine's first Nobel laureate was Emil von Behring (1854-1917). He was the discoverer of diphtheria antitoxin in 1890 and attained a great reputation in his lifetime but also was a subject of controversy:

Behring’s unabashed pursuit of financial rewards for his efforts — unusual in that era—drew much criticism. One of the first modern medical entrepreneurs, he aggressively sought to patent his discoveries, and profited handsomely from their applications. This conflicted with the more genteel notions that prevailed at the time, which venerated physicians as selfless servants of mankind.

For all his accomplishments, Behring was a deeply troubled man. He suffered from frequent bouts of profound depression, and was institutionalised several times.

The great discoverer of serum therapy died of pneumonia in Marburg on March 31, 1917.

References:
Emil von Behring (1854-1917): Medicine's first Nobel laureate. Singapore Med J. 2011 Jan;52(1):1-2 (free full text PDF).