Complex sentence: Boukreev had a reputation as an elite mountaineer in international climbing circles for summiting K2 in 1993 and Mount Everest via the North Ridge route in 1995, but became more widely known for his role in saving climbers during the 1996 Mount Everest disaster.
Split into simpler sentences: Boukreev had a reputation as an elite mountaineer in international climbing circles for summiting K2 in 1993 and Mount Everest via the North Ridge route in 1995. He became even more widely known for his role in saving climbers during the 1996 Mount Everest disaster.