The New York Islanders won four straight Stanley Cups once upon a time and are still the only team to have done so since 1979-80.
Between 1976 and 1979, the Montreal Canadiens won four straight Stanley Cup championships before the New York Islanders matched them between 1980 and 1983. And no other team in the NHL has replicated that since, which is impressive enough.
But do you know what's even more impressive?