It was Wikia member Baku-Cool who gave Valentin 98 the idea for Knightmare. Valentin 98, however, came up with the name.
Knightmare's Bakugan Form was based off a machine named Regalia from the Code Geass franchise.
Ironically, Regalia is part of the group of robots in Code Geass called "Knightmare Frames".
Knightmare really obtained his name from being a combination of horse and knight, despite the fact that he really is a centaur-like Bakugan. Also, his Attribute corresponds with the word "nightmare", which is where his name mainly came from.