J. Welles Wilder Jr. is an American engineer and trader known for his contributions to technical analysis in financial markets. He is best recognized for developing several popular indicators, including the Relative Strength Index (RSI) and the Average True Range (ATR), which help traders assess market trends and volatility. Wilder published his influential book, New Concepts in Technical Trading Systems, in 1978, which introduced his innovative trading strategies. His work has had a lasting impact on the field of technical analysis, and his indicators are widely used by traders and analysts around the world.