How far would you go to protect someone you love? Would you kill large groups of innocent people for medical testing?
That's what Frederick Barnes did on The Blacklist Season 1 Episode 7. In order to find a cure for his son's rare disease, he spread a modified fast-acting version of the disease in a train car that killed everyone on board.
Of course, neither the FBI or Red knew exactly why Barnes went from being a highly respected scientist, to a scientist for hire to the highest bidder, and then finally to someone who distributed his work. Based on this shift, Red called him the "most dangerous man in the world." Based on his intellect, he could cause massive fatalities.