The original (heavy) weight was designed by Bob Newman in the Letraset Type Studio in 1970 [Reichardt]. In 1978, Frankfurter Medium (the only style to include a lowercase, by Alan Meeks) and Frankfurter Highlight (also Meeks?) were added. Frankfurter Inline followed in 1981. [Letraset/MyFonts] Most sources additionally credit Nick Belshaw.
URW had versions named Freyja and Frigorius, including Shadow, Outline, Small Caps and Chrome variants. Latter is Frankfurter Highlight inversed, with an outline.