Chronicling the evolution of a 4th century Byzantine bishop named Nicholas to the 19th and 20th century pop culture icon by the name of Santa Claus would make a fascinating book. Unfortunately, Mr. Seal subscribes to the participatory school of journalism, so this book is about his experience searching for the origins of St. Nicholas via a globe-trotting vacation rather than being about St. Nicholas becoming the legendary figure of Santa Claus.
If the reader is willing to wade through all the autobiography and melodramatic musings, there is some good history on the spread of the cult of St. Nicholas and the development of the legend of Santa Claus. The author's tone is rather pleasant although his long-winded tangents might occasionally cause his audience's eyes to glaze.
If you are interested in reading about how St. Nicholas became Santa Claus without the inclusion of the researcher's life story, then you might want to read WONDERWORKER: THE TRUE STORY OF HOW SAINT NICHOLAS BECAME SANTA CLAUS by Vincent A. Yzermans or ST. NICHOLAS OF MYRA, BARI, AND MANHATTAN by Charles W. Jones. WONDERWORKER is a deceptively simple book. It is short and sweet, and its flaw lies in its lack of citations and bibliography rather than its brevity. ST. NICHOLAS OF MYRA, BARI, AND MANHATTEN is an extremely thorough and well documented but also an extremely scholarly and dry biography of St. Nicholas. Be forewarned that Mr. Jones irreverently refers to St. Nicholas as N. throughout that entire work.
For biographies of St. Nicholas minus Santa Claus, there are ST. NICHOLAS: LIFE, SERVICE, & AKATHIST by St. Dimitry of Rostov and TRANSLATION OF THE RELICS OF ST. NICHOLAS: ACCOUNT AND LITURGICAL SERVICE translated by Isaac Lambertsen. Both of these pamphlets are available from St. John of Kronstadt Press.