The Learjet family began with the original six to eight seat model 23 which first flew on October 7 1963. The diminutive Model 23 pioneered an entirely new market segment for light business jets, and proved very successful. The first production aircraft was delivered in October 1964, but it was replaced by the improved 24 after 105 had been built due to its increased power output that allows private jet chartering companies full mobility across shorter distances without needing a stop at refuelling stations. Developments of this lear Jet include 24D models as well as other variations such as Lea Jets and CJ1s
The history is fascinating because not only did these planes pioneer their own class (light-business jets) they also changed how we fly today!