"That's Frank and Alice Longbottom-- poor devils. Better dead than what happened to them …"
-- Mad-Eye Moody (OP9)
Frank Longbottom, along with his wife Alice, were famous Aurors who fought valiantly against Voldemort and his supporters during the 1970s. Frank and Alice were members of the original Order of the Phoenix (OP9, PC/JKR1). They were captured by Bellatrix Lestrange, Barty Crouch Jr., and several other Death Eater shortly after the fall of Voldemort (late 1981) and tortured using the Cruciatus Curse in an attempt to force them to tell the whereabouts of the defeated Dark Lord. The torture drove them insane and are now at St. Mungo’s Hospital for Magical Maladies and Injuries in Ward 49. They do not even recognize family members, including their son Neville. (GF30, OP23).
The character of Frank Longbottom only appeared in the film in the photograph of the Order of the Phoenix. In that photo, Frank was played by James Payton (Pm).
From the Web
The Longbottom Family Reunion on the Set of Fantastic Beasts from Pottermore.
Unsung Heroes: Colin Creevey & Frank Longbottom by daintydangerous