K2, at 8,611 metres (28,251 ft) above sea level, is the second-highest mountain on Earth, after Mount Everest at 8,849 metres (29,032 ft). It lies in the Karakoram range, partially in the Gilgit-Baltistan region of Pakistan-administered Kashmir and partially in the China-administered Trans-Karakoram Tract in the Taxkorgan Tajik Autonomous County of Xinjiang.

K2 also became popularly known as the Savage Mountain after George Bell—a climber on the 1953 American expedition—told reporters, "It's a savage mountain that tries to kill you." Of the five highest mountains in the world, K2 is the deadliest; approximately one person dies on the mountain for every four who reach the summit. Also occasionally known as Mount Godwin-Austen, other nicknames for K2 are The King of Mountains and The Mountaineers' Mountain, as well as The Mountain of Mountains after prominent Italian climber Reinhold Messner titled his book about K2 the same.

Although the summit of Everest is at a higher altitude, K2 is a more difficult and dangerous climb, due in part to its more northern location, where inclement weather is more common. The summit was reached for the first time by the Italian climbers Lino Lacedelli and Achille Compagnoni, on the 1954 Italian expedition led by Ardito Desio. As of February 2021, 377 people have summited K2. There have been 91 deaths during attempted climbs.

Most ascents are made during July and August, typically the warmest times of the year. But in January 2021, K2 became the final eight-thousander to be summited in the winter; the mountaineering feat was accomplished by a team of Nepalese climbers, led by Nirmal Purja and Mingma Gyalje Sherpa.

K2 has now been climbed by almost all of its ridges, but unlike other eight-thousanders, never from its eastern face.