Yogi Ramacharaka was the pseudonym of William Walker Atkinson, an American writer who was influential in turn-of-the-century (1890s-1900s) spiritual/philosophical movements such as 'New Thought' (a precursor to today's New Age movement) and Theosophy.
Atkinson, writing as Ramacharaka, helped to popularize Eastern concepts in America, with Yoga and a broadly-interpreted Hinduism being particular areas of focus. Ramacharaka's Advanced Course in Yoga Philosophy and Oriental Occultism remains widely respected as an excellent primer for the Western layman, despite the fact that it reached 100 years old in 2004 and is understandably dated in some respects.
There are a number of other Ramacharaka works, in addition to several popular books written by Atkinson under his own name. Many of Atkinson's works sold well at the time of their publication, although he has not been favored with significant historical recognition. This may be due to the fact that many of his books dealt with ideas now widely discredited as pseudoscientific, such as mentalism. There is some debate as to whether other authors may have contributed to the Ramacharaka books, but reliable information relating to Ramacharaka/Atkinson is scarce.
William Walker Atkinson died in 1932, in Los Angeles, California after successful careers in writing and law. He is now largely forgotten, despite obtaining mention in past editions of Who's Who in America, Religious Leaders of America, and several similar publications.
Titles by Ramacharaka/Atkinson can be found in a Brazilian organization Círculo de Estudos Ramacharaca (Ramacharaka Studies Circle) and from the American publisher: Kessinger Publishing's Rare Reprints.
One person has done some fairly extensive research into the mystery of "Who was Yogi Ramacharaka?" One of the possibilities explored is that Atkinson may have been ghost writing for another person when he authored books under the name of "Yogi Ramacharaka." The results of this personal quest for information are available online (approx. 8 pages if you make a hard copy.) See the external link: "Who was Yogi Ramacharaka?"