The Beech Model 90 King Air was the first model in the largest and most successful family of corporate turboprop twins yet built.

The King Air began life as a turboprop development of the Queen Air designed to meet a US Army requirement for a staff/utility transport. A prototype PT6 powered Queen Air Model 65-80 (later 65-90T) began test flying in 1963 and the type was subsequently ordered by the US Army in unpressurised form as the U-21A.

The civil equivalent, the Model 90 King Air, introduced pressurization and first flew on January 20 1964. Deliveries of production civil aircraft began in late 1964.

Development resulted in several civil variants, including the A90 and B90 with PT6A-20 engines; the C90 with PT6A-21s; the E90 with more powerful PT6A-34Bs; and the F90 which introduced the T-tail of the 200 (described separately), four blade props and other modifications. The less expensive C90SE Special Edition was released during 1994, but is no longer offered. The current C90B has been in production since 1991.

The Model 100 is a stretched derivative of the Model 90 featuring five cabin windows instead of the Model 90's three; MTOW increased by 1,300 lb (590 kg) over the 90, to 10,600 lb (4,810 kg). The 100 used the wings, tail, and engines (two PT6A-28 engines rated at 620 shp) from the Model 99 airline, itself a development of the Queen Air.