Jamie Coots, pictured above, is one of the most well known snake handlers and will appear in a National Geographic series about snake handling called "Snake Salvation" and premiers this fall.
According to NPR, snake handlers look to the 16th chapter of Gospel of St. Mark. "And these signs shall follow them that believe; in my name shall they cast out devils; they shall speak with new tongues; "They shall take up serpents; and if they drink any deadly thing, it shall not hurt them; they shall lay hands on the sick, and they shall recover."
Here's a clip from CNN about snake handling that I found last year.
Mack Wolford, a Pentecostal pastor and snake handler died last year after being bitten by a rattle snake and refusing healthcare. Here is the Washington Post story.