The Jedi Knight series primarily focuses on mercenary/ Jedi Knight Kyle Katarn starting with Star Wars: Dark Forces and then continuing on with it's own series titled Star Wars: Jedi Knight.
When Dark Forces was being developed the idea was to have Luke Skywalker be the main character but with a limited story Kyle Katarn was created as a quick replacement. Like with many Star Wars games everyone may have enjoyed the Dark Forces game but fans still wanted to play as a true Jedi. Before the release of Dark Forces, Katarn's continuing story was already being discussed and this included the addition of the force and a lightsaber.
Despite the clear success of both Dark Forces games a new game wouldn't be released until 2002, a full six years after Dark Forces 2. The development of the new game was given to an outside studio, Raven Software, and Star Wars Jedi Knight 2: Jedi Outcast. Despite the change of developer and continuing evolution of the series from a Doom-like first person shooter to a first/third person Jedi game, Jedi Outcast was highly received. So much so that Lucas Arts allowed Raven to continuing development of the series and they made Star Wars Jedi Knight: Jedi Academy only two years later.
As of September 16th, 2009, all five Jedi Knight games are made available in Steam and Direct2Drive.