The Kripke era refers to the seasons of Supernatural helmed by its creator, Eric Kripke and co-showrunner Robert Singer. It encompasses Season 1 up to Season 5. The first five seasons contain the exposition of the main characters of the show, and, although contained season-long story arcs, actually built up to a climactic five-season arc about supernatural forces working to usher in the Apocalypse. Kripke himself originally named the plan for his show the "five-year plan", covering the first five seasons of the show, all leading up to the events in Swan Song. The show was supposed to end at this point but Kripke handed over the role as showrunner to Sera Gamble for Seasons 6 and 7.
|“||When you start a show, the plans are not set in stone. They're really mutable, cocktail napkin sketches. I had a plan about demons. That was my plan when I began. When we were starting to figure out, somewhere around the pilot, that this was becoming a series, one of the producers and I were kicking around a game plan, and it was about demons. We started with this demon, and this demon worked for that demon, and that demon wanted to let the devil loose. It was all about working our way up the demon ladder. I'm not even sure we knew that, at that time, Yellow Eyes was working for Lilith. We just knew that there was a higher demon. And then, we decided to make her a woman because the first demon was a man. So, these things evolved. We had a structure of a demon ladder that was ultimately about letting Lucifer loose and having him take over Sam. The dark secret was always that Sam was going to be the vessel. Originally, it was just that Dean would then have to hunt down and kill his brother. But then, rightfully so, we brought in angels to bolster up the other side of the coin. And then, Michael came into the story. It evolved from just, "I have to hunt down and kill my brother," to these two mirrored stories about two sets of brothers, the brothers in Heaven and the brothers on Earth, and how they compare and contrast. A lot of it was dumb luck, and a lot of it was noticing the opportunities that we had in front of us, at the time, and taking advantage. For the most part, it worked out.||”|
— Eric Kripke 
|“||People don't remember that we were within an inch of cancellation the first three or four years we were on the air. We always had to fight to stay on and in season two, that was very true. We moved over, it was the new CW and we were a bubble show. A big note that the network had at the time was "we should really give the boys a home and some recurring characters, and bringing in some women would be good."||”|
— Eric Kripke 
The plot of this era revolves around a conflict between the angels led by the archangel Michael, and the demons of the fallen archangel Lucifer, and their respective predestined vessels, Sam and Dean Winchester.
Azazel, a powerful yellow-eyed demon sought to release Lucifer from his cage, and orchestrated a complex plan that will create possible vessels that will host Lucifer when he is freed from the cage. His plan also simultaneously allowed the release of an army of demons onto earth to prepare for the war, and also to secure a righteous man that will spill blood in hell, which begins the many steps leading to the eventual escape of Lucifer.
At this point, the angels were sent down to Earth in an attempt to stop the release of the fallen archangel Lucifer. However, the highest members in command of the heavenly host actually plan to let Lucifer be set free so they could usher in the Apocalypse and, assuming that the Angels won the war, paradise would follow. Angels of lower commands were not privy to this, and some of the angels actually worked with the plan to release Lucifer.
The Era ended with the apocalypse being averted by Sam, Dean, Castiel and Bobby Singer, and with the leaders of the two warring factions, also the two most powerful Archangels in existence, trapped and basically incapacitated inside Lucifer's cage.