Grumman developed the Gulfstream I turbine powered executive transport to replace the many hundred war surplus piston twins performing such missions in the mid 1950s.
Design work began in 1956, with ... first flight of the Gulfstream I prototype occurring on August 14 1958. FAA Type certification was awarded on May 21 1959 and deliveries of production aircraft followed from that June. Notably, the Gulfstream I was the first US twin engined corporate transport to be certificated to cruise at 30,000ft.
[Text and Photo provided by Airliners.net: http://www.airliners.net/aircraft-data/stats.main?id=236 ]