If you caught leprosy in the 12th century, your career paths were limited to "boogeyman" and "cautionary tale." People were so scared of catching it that lepers were banished from society and forbidden to mix with healthy people. The Order of St. Lazarus was a leper hospital in Jerusalem dedicated to caring for knights who had been stricken with the disease. The Templars would send leper knights there and pay for their care -- it was like a medieval VA hospital. Well ... like a slightly more medieval VA hospital, at any rate.
Every Leper's Day, they'd reminisce about the Gross War and World War Eww.
But when the Crusades escalated and the Ottoman hordes came knocking on Jerusalem's door, the leper knights weren't about to take it lying down. Instead of waiting to fall to pieces while their healthy cohorts did God's work, the Order of St. Lazarus donned their armor again, picked up their broadswords, and entered the fray.
The leper knights weren't particularly successful in their campaigns, but they earn points for having giant balls (assuming that they hadn't fallen off yet). That doesn't mean they weren't formidable opponents, though. Imagine a bunch of dudes who know they're going to die soon anyway, who can't feel pain due to nerve damage, and who are basically walking biological weapons. Actually, if you can wait a year or so, you won't have to imagine it -- that is, if Hollywood picks up our badass new screenplay, Knight Of The Lepers.