Besides his worldwide mountain climbing experience, Whittaker became the most experienced glacier-travel guide by climbing Mount Rainier with over 250 summits. He also established Rainier Mountaineering, developed a group of successful climbing-related businesses at the Rainier Base Camp in Ashford, adjacent to Mount Rainier National Park. There he led the training of several generations of Rainier guides, many of whom continue to guide and climb elsewhere. He also led the first American ascent of the North Col of Mount Everest in 1984.