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Jaeger was born in 1946 in Boulogne-Billancourt, France, the son of photographer Janine Niépce. He made more than 100 solo ascents in the Mont Blanc massif, including more than a dozen first ascents.
Jaeger became a mountain guide in 1975. On October 15, 1978, he participated in the first French ascent of Mount Everest. The team leader was Pierre Mazeaud. Other team members included Jean Afanassieff and Kurt Diemberger. Jaeger and Afanassieff were the first to climb and then ski down one of the 14 mountains on Earth higher than 8,000 metres (26,000 ft). From July 27 to September 27, 1979, he spent 60 days alone at 6,700 metres (22,000 ft) altitude on Huascarán to study the effects of "super-acclimatisation" on himself. He published an account of his experience in Carnets de Solitude the same year.
First solo ascents
- 1972 – Arête Sans Nom on the Aiguille Verte
- 1972 – North spur of Les Droites
- 1973 – North–south traverse of the Chamonix Aiguilles
- 1975 – Bonatti–Gobbi route on the Grand Pilier d'Angle