Rick and Morty Theory: Morty and Diane's death create.
My theory is that Rick became the way he is because of both Morty and Diane’s death.
In Season 9, Episode 10, we see that Rick was sober and doing perfectly fine without a Morty. However, once a Morty entered his life, Rick slowly became more like the “regular” Ricks we know. Sober Rick’s wife even says something along the lines of Morty “poisoning his mind,” which could be an important clue.
I think Morty being around Ricks is one of the main reasons Rick eventually became the Rick we know. Rick had already wanted to create a portal gun before Morty came into his life, just like other Ricks. However, when Morty wanted to get home, Rick started working on the portal gun again. Doing this may have caused him to relapse into drinking, which slowly pushed him back toward becoming a more typical Rick.
So, my theory is that Diane’s death and Morty’s presence are the two major factors that shaped Rick into the person he became. Diane’s death caused the original trauma, while Morty’s arrival may have triggered Rick’s return to the unhealthy habits and personality that define the “Rick” we know.
Also during that episode, as Sober Rick drink, he became more like Ricks, saying very cokcy stuff.