The summit of the world's tallest mountain has been the ultimate challenge for climbers for over a century. Who were the five greatest Everest climbers of all time? While others have climbed it more often, these are the ones whose names deserve to be in the history books.

01 of 05 George Mallory: Mount Everest's Most Famous Climber Photograph courtesy John Noel/Timesonline In 1924, 37-year-old George Leigh Mallory (1886-1924) was perhaps Britain's most famous mountaineer. The handsome, charismatic, ex-schoolteacher was already a seasoned Himalayan veteran, having been part of the 1921 British Reconnaissance Expedition to Mount Everest and then a serious attempt on the mountain in 1922, which ended in disaster with the deaths of seven Sherpas in an avalanche. Mallory did, however, break the 8,000-meter barrier, climbing to 26,600 feet without supplemental oxygen. Two years later George Mallory's name was on the list for the 1924 Everest expedition. He had great hopes for success on the world's highest mountain, despite a premonition that he wouldn't return home from another attempt to his wife Ruth and three small children. Mallory, with a better understanding of the monsoon weather, felt the group had a good chance of success. He wrote Ruth from Everest base camp: "It is almost unthinkable with this plan that I shan't get to the top" and "I feel strong for the battle but I know every ounce of strength will be wanted." The expedition's first summit attempt was by Major Edward Norton and Theodore Somervell on June 4. The pair set off from Camp VI at 27,000 feet and labored up strenuous terrain without oxygen to 28,314 feet, a high-altitude record that stood for 54 years. Four days later George Mallory teamed up with young Sandy Irvine for a summit try using oxygen canisters. Last Seen Alive On June 8 the pair set off up the Northeast Ridge, plodding upward at a good pace. At 12:50 p.m. Mallory and Irvine were last seen alive by expedition geologist Noel Odell who spotted them through a break in the clouds on the Second Step, a rock outcrop on the ridge. Odell then climbed up to Camp VI and squatted in Mallory's tent in a snow squall. During the quick-moving storm, he stepped outside and whistled and yodeled so the descending climbers could find the tent in the white-out. But they never returned. Whether George Mallory and Sandy Irvine were able to climb to the summit of Mount Everest on that June day has been an enduring mystery of Everest mountaineering. Some of their gear was found over the ensuing years, like Irvine's ice axe in 1933. Then Chinese climbers reported seeing the bodies of English climbers during the 1970s. Discovery of Mallory's Body In 1999 the Mallory and Irvine Research Expedition was able to locate Mallory's body along with some of his personal effects including goggles, altimeter, knife, and a stack of letters from his wife. The party was unable to locate his camera, which might provide clues to the mystery. They did surmise that the fatal accident happened on the descent and probably in the dark since the goggles were in Mallory's pocket and that the two were roped together. So the mystery of George Mallory remains. Did Mallory and Irvine fall while descending from the summit or were they retreating after a failed attempt? Only Mount Everest knows and it holds the secret close.

02 of 05 Reinhold Messner: Everest Climbing Visionary Photograph courtesy Reinhold Messner/Rolex Reinhold Messner, born in 1944 in the Italian province of South Tyrol, is simply the greatest of the Mount Everest climbers. He began climbing in Italy's Dolomites, reaching his first summit at age 5. By the time he was 20 years old, Messner was one of the best European rock climbers. He then turned his attention to the great faces in the Alps and then the great mountains of Asia. Climbing Everest Without Supplemental Oxygen Messner, after climbing Nanga Parbat in 1970 with his brother Günther, who died during the descent, advocated that Mount Everest should be climbed without the use of supplemental oxygen or by what he called "fair means." The use of oxygen, Messner reasoned, was cheating. On May 8, 1978, Messner and climbing partner Peter Habeler became the first climbers to reach the summit of Everest without bottled oxygen, a feat that some doctors thought impossible since the air is so thin and that climbers would suffer brain damage. On the summit, Messner described his feelings: "In my state of spiritual abstraction, I no longer belong to myself and to my eyesight. I am nothing more than a single narrow gasping lung, floating over the mists and summits." New Solo Route up Everest Two years later on August 20, 1980, Messner again stood atop Mount Everest without oxygen after climbing a new route up the North Face. For this audacious ascent, the first solo new route on the mountain, Messner traversed across the North Face, and then climbed the Great Couloir directly to the summit, avoiding the Second Step on the Northeast Ridge. He was the only climber on the mountain and spent only three nights above his advanced base camp below the North Col. Messner Climbs All 14 Eight-thousanders In 1986 Reinhold Messner became the first person to climb the 8,000-meter peaks, the 14 highest mountains in the world, after reaching the summits of Makalu and Lhotse, the last 8,000-meter peaks he climbed in his storied career.

03 of 05 Sir Edmund Hillary: New Zealand Beekeeper Makes Everest First Ascent Photograph courtesy Edmund Hillary Sir Edmund Hillary (1919-2008) and Sherpa teammate Tenzing Norgay were the first recorded climbers to reach the rarefied summit of Mount Everest on May 29, 1953. Hillary, an unassuming lanky New Zealand beekeeper, had first traveled to the Himalayas in 1951 as part of an expedition led by Eric Shipton that explored the Khumbu icefall. He was asked to return to Everest on the ninth British expedition to the mountain and was paired up with Tenzing for a summit bid by leader John Hunt. On May 29, after spending two hours to thaw his frozen boots, the duo left their high camp at 27,900 feet and climbed to Mount Everest's summit, passing the Hillary Step, a 40-foot cliff above the South Summit. While Hillary maintained that the two reached the summit at the same time, Tenzing later wrote that Hillary was first to step onto the top at 11:30 a.m. After taking photographs to verify that they had indeed reached the roof of the world, they descended after spending 15 minutes on top. The first person they met on the mountain was George Lowe, who was climbing up to meet them. Hillary told Lowe, "Well George, we knocked the bastard off!" Off the mountain, the always-smiling and congenial pair of climbers received worldwide acclaim as mountaineering heroes. Edmund Hillary was knighted by young Queen Elizabeth II just after her coronation, along with leader John Hunt. Hillary later devoted his life to digging wells and building schools and hospitals for the Sherpas in Nepal. Ironically, he discovered a few years after climbing Mount Everest that he was prone to altitude sickness, ending his high-altitude climbing career.

04 of 05 Tenzing Norgay: Sherpa to the Top of the World Photograph courtesy Sir Edmund Hillary/Tenzing Norgay Tenzing Norgay (1914-1986), a Nepalese Sherpa, reached the summit of Mount Everest with Edmund Hillary on May 29, 1953, with the pair becoming the first people to stand on top of the world. Tenzing, the 11th of a family with 13 children, grew up in the Khumbu region in the shadow of Mount Everest. In 1935 at age 20 Tenzing joined his first Everest expedition, a reconnaissance of the region led by Eric Shipton, and worked as a porter on three other Everest expeditions. In 1947 Tenzing was part of a group attempting to climb Mount Everest from the north but failed due to bad weather. In 1952 he worked as a Sherpa climber on a couple of Swiss expeditions that made serious attempts on Everest from its Nepal side, including what became today's standard South Col route. On the spring attempt, Tenzing reached 28,200 feet (8,600 meters) with Raymond Lambert, the record highest elevation reached at that time. The following year, 1953, saw Tenzing on his seventh Everest expedition with a large British group led by John Hunt. He was paired with New Zealand climber Edmund Hillary. They made the team's second summit attempt on May 29, climbing from a high camp past the South Summit, surmounting the Hillary Step, a 40-foot-high cliff, and scrambled up the final slopes, reaching the summit together at 11:30 a.m. Norgay later ran trekking adventures and was an ambassador of Sherpa culture. Tenzing Norgay died at age 71 in 1986.