Storm Chasers are people from all walks of life who have an interest in meteorology and weather forecasting. Unlike normal sane people, who run away / lock themselves in the basement when a twister comes close, they take this interest to the extreme by chasing tornadoes around and getting as close as possible to them before taking photographs, shooting videos, and trying to take readings of the forces holding the funnel together.
There are estimated to be 50 - 100 regularly active storm chasers in the USA, centred around western Oklahoma and the Texas panhandle. Storm chasing is widely regarded to have started by Dave Hoadley, Roger Jensen, and Neil Ward in the 1950's and has recently come into the media spotlight after the Jan de Bont movie 'Twister' came out in 1996.
Research taken from www.imdb.com, www.stormtack.org and www.stormchase.com