Johan first began mountain climbing in 1964 in the Alps and in the mid-1970s in the Himalayas, including participating on the successful 1976 American Everest Expedition and making a first ascent in 1979 of the South Face of Buni Zom (21,500 ft) in the Hindu Kush (Pakistan). His climbs in the Andes began in 1980 with ascents of mountains in Ecuador, and he eventually climbed the majority of Andean peaks over 6,500 m (21,325 feet)—several of them solo. A historian of Andean ascents for the American Alpine Club noted in the early 1990s that Johan had climbed more high-altitude Andean peaks (over 20,000 feet) than any other person.