: J. Welles Wilder Jr., the inventor of the Relative Strength Index (RSI).
The search for an typically leads traders to one of two paths: the foundational classics that defined technical analysis or modern tactical guides that offer specific strategies for today's volatile markets. The Foundational RSI Book rsi pdf book
: Wilder defined the RSI as a momentum oscillator that measures the speed and change of price movements on a scale of 0 to 100. : J. Welles Wilder Jr.
If you are looking for the original source, the most important "RSI book" is by J. Welles Wilder Jr. (1978). rsi pdf book