Yoichi Hiraoka was an amazing Japanese xylophone player who had significant influence on the development of the xylophone as a solo instrument. The purpose of this dissertation is to collect and record evidence of Mr. Hiraoka, to examine his distinguished efforts to promote the xylophone, to investigate his influences on keyboard percussion literature, and to contribute to the development of the art of keyboard percussion performance as a whole. This dissertation addresses Yoichi Hiraoka’s artistic life, his commissioned pieces, and his influence on the art of xylophone performance. Analyses of two of his most influential commissioned works, Alan Hovhaness’ Fantasy on Japanese Wood Prints and Toshiro Mayuzumi’s Concertino for Xylophone Solo and Orchestra, are also included to illustrate the art of the xylophone, and to explain why Hiraoka did not play all of his commissioned works.