The name of the firm, KPMG, is not actually an initialism. However, the roots of the name stem from four partners in the firms that merged to form KPMG.
K stands for Klynveld. This originates from the accounting firm Klynveld Kraayenhof & Co. founded by Piet Klynveld in Amsterdam in 1917.
P is for Peat, originating from the accounting firm William Barclay Peat & Co., which was founded by William Barclay Peat in London in 1870.
M stands for Marwick. James Marwick founded the accounting firm Marwick, Mitchell & Co. together with Roger Mitchell in New York City in 1897.
G is for Goerdeler. Dr. Reinhard Goerdeler was for many years chairman of the German Deutsche Treuhand-Gesellschaft (DTG) and later chairman of KPMG. He is credited with laying much of the groundwork for the KMG merger.