"... Initial speculation pointed to John Carmack as the probable author of the code, but the original authors were much earlier in 3D computer graphics. Rys Sommefeldt concluded that the original algorithm was devised by Greg Walsh at Ardent Computer in consultation with Cleve Moler, the creator of MATLAB. Cleve Moler learned about this technique from code written by William Kahan and K.C. Ng at Berkeley around 1986." - https://en.wikipedia.org/wiki/Fast_inverse_square_root