Regarding who designed them, the original library was (not surprisingly) created by Bjarne Stroustrup, and then reimplemented by Dave Presotto. This was then redesigned and reimplemented yet again by Jerry Schwarz for Cfront 2.0, using the idea of manipulators from Andrew Koenig. The standard version of the library is based on this implementation.
Source “The Design & Evolution of C++”, section 8.3.1.