That's Grizzly Adams on the right
In 1855, Adams suffered head and neck trauma during a grizzly attack in the Sierra of California. His scalp was dislodged, and he was left with a silver dollar-sized impression in his skull, just above his forehead. Adams had made pets of several grizzlies, and often wrestled with them while training them and in exhibitions. During one such bout, his most delinquent grizzly, General Fremont (named for John C. Fremont), struck Adams in the head and reopened the wound. It was subsequently reinjured several times, eventually leaving Adams' brain tissue exposed.
The damage was further exacerbated while Adams was on tour with a circus in New England during the summer of 1860, when a monkey he was attempting to train purportedly bit into the wound. After more than four months performing with his California Menagerie, complications from the injury led to Adams' inability to continue with the show. After completing his contract with P.T. Barnum, he retired to Neponset, Massachusetts, where he died of illness (possibly meningitis) just five days after arriving at the home of his wife and daughter.