Hedge-fund icon Stanley Druckenmiller is shutting his firm and ending a 30-year career after amassing one of the best long-term trading records in the industry and generating $1bn for George Soros by forcing a devaluation of the British pound. Druckenmiller, 57, said he was tired of the stress of managing money for others and frustrated by his failure in the past three years to match returns that had averaged 30 percent annually since 1986.