Jeremiah Stewart writing over at Coffee With Kenobi look at the original theft of the Death Star plans as told in the Legends/EU era.
So here is what we knew before, according to Legends.
First of all we had Dark Forces, the Doom clone by Lucasarts, which introduced Kyle Katarn, who was sent on a mission as a double agent, to capture the plans of the Death Star. In the game, this is just part of the overall plot (about half), and we get to see the event of him capturing the plans
There are plenty more elements to the wider story, so click here and check out this excellent article.
