Introduction to Relative Strength Index by Mudrex.com The RSI was created by Welles Wilder and many trading strategies have  been designed around this indicator.  It is intended to chart the  current and historical strength or weakness of a stock or market based  on the closing prices of a recent trading period. From trading oversold  and overbought levels to trend determination via the 50 level, the RSI  momentum indicator makes up the backbone of many different types of  strategies.