Mihaly Csikszentmihalyi, PhD,  (pronounced me-high chick-sent-me-high) is a psychology professor at Claremont Graduate University in Claremont, California, and former head of the department of psychology at the University of Chicago. He is noted for his work in the study of creativity and subjective well-being, and for his research and writing on the notion of flow. [From Wikipedia bio.]

Also see related articles [by Douglas Eby]: Creativity and Flow Psychology, and The science of feeling good.