[NOTE: This article has been updated with more timelines previously missed.]
While we still have a few days before The Flash and company return to finish off their seasons, there are still some people who don't completely understand the timelines #TheFlash takes place in. Here is a quick guide to follow the ever-changing timelines. Mind you, this guide does not include #LegendsOfTomorrow, for that is a whole other animal.
The Original: 2020–2024
Way back in the pilot of The Flash we were introduced to Eobard Thawne as Harrison Wells. In his Time Vault we see a newspaper article dated April 25, 2024 (by the way thats when The Flash comes back, and it's the episode where he goes to the future). This is the Original timeline, where Barry became the Flash in 2020. We don't know much about it except that Barry and Iris are married, Caitlin is still Killer Frost, and Bruce Wayne and Oliver Queen are business partners. While we still have to wait until Tuesday to find out more about the original timeline, I'm sure we will learn more.
Alternate Original: 2000–2016
This is the timeline most people are familiar with. This timeline takes place during Season 1 and 2. In this timeline, Eobard Thawne travels back in time to kill Barry, his greatest enemy, but ends up killing his mother instead. Eobard succeeds, but is stuck in the past. In order to get back to the future he must create the Flash, and fast (pun intended).
So, Thawne became Harrison Wells and created the Particle Accelerator explosion in 2014 to create the Flash.
In Season 1, Barry time traveled for the first time while battling the Weather Wizard. Weather Wizard created a tsunami that would of destroyed Central City. In order to stop it Barry had to run faster to build up a barrier which caused him to time travel back a day before. He proceeded to stop the Wizard before he attempted anything. However, Captain Cold and Heat Wave cause another bad situation.
In the second crossover event during a fight with Vandel Savage, Barry outruns a blast that kills all the other heroes, including Oliver. Barry continues to the day before to warn everyone of their death.
This did little to change the timeline. In Season 2, Barry travels back in time to Season 1 to talk to Eobard Thawne. The purpose of this particular mission was to find the Reverse Flash to figure out how he was able to run so much faster than Barry. He interacted with his past self to stop the Pied Piper. The only change this causes is that when Barry returns to the present, the Pied Piper is on the good side.
At the end of Season 2, Barry decided to go back in time and save his mother. This, of course, changed the timeline. Since his mother is alive, his father never went to jail for her murder. In Flashpoint, he never got close to Iris and Joe, Wally is the [Kid] Flash, and Cisco is a billionaire running Star Labs. For three months, Barry lived in this alternate timeline with his parents. He was happy. For the first time Barry wasn't scared; he had his family back.
However, it came with a price. Barry started to lose his memories from his timeline, and they were being replaced with memories from Flashpoint. Plus, he was losing his speed. Barry then realized what he had done, and sought help from Thawne, whom he kept locked away. Thawne told Barry what was happening and how to get back. Barry agreed and went to his parents to say goodbye for the final time.
Before that, however, he helped Wally with his Reverse Flash, The Rival, but it ended in Wally's death. This was his final push to restore the timeline. He and Thawne traveled back to the night where Barry's mother died and Thawne killed her. Again.
This leads to...
Here we are at the current timeline, post-Flashpoint. This timeline is different from the Alternate Original. Barry came back and everything seemed fine, until he realized the team wasn't the same. Cisco couldn't bare to look at Barry because Cisco's brother died and Barry wouldn't go back and save him. Iris and Joe weren't talking, and there was a new string of metahumans from Flashpoint that started to pop up. The changes, however, didn't stop there. In Arrow, Diggle has a boy, whereas in the Alternate Original, he had a girl. As the season finishes, hopefully there will be more changes that remain within the confines of The Flash TV show.
Another Possible Timeline?
With Legends and The Flash, its entirely possible for there to be other timelines. Moreover, with Season 3 coming to a close, maybe Barry will try to fix the post-Flashpoint timeline. Or, maybe not — it's up to him.
I hope this quick guide helps you understand where we are in the Arrowverse. We will just have to see when it changes again.