Most influential American climber of the 20th Century...

The fact that Americans are so self-focused and insular is something I have to live with constantly. I'm always reminded of it by non-Americans.

" ... epitome of the "all rounder" with demonstrated skill in rock, ice, mixed and alpinisim.

Robert Lindley Murray Underhill (March 3, 1889 – May 11, 1983) was an American mountaineer best known for introducing modern Alpine style rope and belaying techniques to the U.S. climbing community in the late 1920s and early 1930s.

He was a longtime member of the Appalachian Mountain Club and editor of its journal Appalachia from 1928 to 1934.[3]

On August 4, 1928 Underhill, accompanied by Miriam O'Brien and guides Armand Charlet and G. Cachat, completed the first ascent of the traverse from the Aiguilles du Diable to Mont Blanc du Tacul in the Alps.[4] This route involves "climbing five outstanding summits over 4000 meters in superb surroundings."[5] On this same trip, Underhill completed guided ascents of the Peuterey and Brenva ridges of Mont Blanc. His climbing partner Miriam O'Brien was later to become his wife, and a famous mountaineer in her own right.

Underhill and Kenneth Henderson were responsible for introducing technical mountaineering to Grand Teton National Park in 1929, the year the park was formed. They completed the first ascent of the east ridge of the Grand Teton.

In 1930, he returned to the Tetons, and was unsuccessful in a solo attempt on the North Ridge of the Grand Teton.

His article On the Use and Management of the Rope in Rock Work was published in the Sierra Club Bulletin in February, 1931. This influential 22 page article covered rope use, knots, belaying, "roping down" (now called rapelling or abseiling), and the use of slings. Writing during a period when many climbers still resisted such safety innovations, Underhill described roped team climbing as "one of the finest experiences that mountaineering can afford."[6]

He was back in the Grand Tetons for six weeks the summer of 1931, completing on July 15 a first ascent of the southeast ridge of the Grand Teton, a route which now bears his name. On July 19, 1931, Underhill and park ranger Fritiof Fryxell completed the "remarkable" first ascent of the North Ridge of the Grand Teton, which is rated IV, 5.7 in the Yosemite Decimal System.[7]

Departing Wyoming, Underhill went on to California at the invitation of Sierra Club leader Francis P. Farquhar, for the purpose of teaching the most advanced techniques of roped climbing and belaying developed in the Alps. Underhill began by instructing a group of Sierra Club members in those techniques in the Minarets, practicing on the slopes of Mount Ritter and Banner Peak.[8] After this introductory course, an advanced group led by Underhill and including Norman Clyde, Jules Eichorn, Lewis Clark, Bestor Robinson and Glen Dawson traveled south to the Palisades, the most rugged and alpine part of the Sierra Nevada.[9] There, on August 13, 1931, this party completed the first ascent of the last unclimbed 14,000+ foot peak in California, which remained unnamed due to its remote location above the Palisade Glacier. After a challenging ascent to the summit, the climbers were caught in an intense lightning storm, and Eichorn barely escaped electrocution when "a thunderbolt whizzed right by my ear". The mountain was named Thunderbolt Peak to commemorate that close call.

Three days later on August 16, Underhill, Clyde, Eichorn and Dawson completed the first ascent of the East Face of Mount Whitney, the highest peak in the contiguous United States.[10] By California standards at that time, the route was considered extremely exposed, especially the famous Fresh Air Traverse.[11] Steve Roper called this route "one of the classic routes of the Sierra, partly because of its spectacular location and partly because it was the first really big wall to be climbed in the range."[12] Porcella & Burns wrote that "the climb heralded a new standard of technical competence in Californian rock climbing."[13] Underhill himself commented that "the beauty of the climb lies chiefly in its unexpected possibility, up the apparent precipice, and in the intimate contact it affords with the features that lend Mount Whitney its real impressiveness."[14]

Bestor Robinson described Underhill's influence on California rock climbing in a 1934 Sierra Club Bulletin article: "The seed of the lore of pitons, carabiners, rope-downs, belays, rope traverses, and two man stands was sown in California in 1931 by Robert L. M. Underhill, a member of the Appalachian Mountain Club, with considerable experience in the Alps. That seed has sprouted and grown in California climate with exuberant vigor sufficient to satisfy the most vociferous Chamber of Commerce."[15]

He married mountaineer Miriam O'Brien on January 28, 1932, and they had two sons, Robert and Brian, born in 1936 and 1939. After World War II, he climbed with his wife in the Wind River Range of Wyoming, the Mission, Swan and Beartooth ranges of Montana, and the Sawtooth range of Idaho.

without that qualifier i'm sticking with ms. hill.