Oscar Eckenstein (9th September 1859 - 1921) was an Anglo-German rock-climber and mountaineer. He was one of the few people who readily climbed with Aleister Crowley, with whom he made an early expedition to K2. He also climbed in the Lakes with the Abrahams, though their relationship was not always smooth, and in North Wales with G. W. Young and J. M. Archer Thomson. Aleister Crowley Aleister Crowley, born Edward Alexander Crowley (12 October 1875 - 1 December 1947) was an occultist, mystic, sexual revolutionary, and drug user (especially heroin). ... George and Ashley Abraham were two climber-photographers, who lived in Keswick, in the Lake District; they made a photographic record of many of the climbing pioneers, such as O G Jones, and their climbs, including themselves on their own routes. ...

He was technically very proficient, an early advocate of 'bouldering', but rarely led. He was an early advocate of balance-climbing, using small holds.

He is credited with designing the modern crampon and to have developed the use of the short ice-axe.