Yes, PokerStars is 100% legit, and it first launched as an online poker site in 2001. Is PokerStars Casino rigged? No, all the PokerStars Casino games undergo tests and verifications. Also, the site is licensed and regulated, ensuring fair play at all times.
PokerStars is one of the few poker sites out there who are very open about what they do. They will in fact actually send you every single hand history that you have ever played on their site. I know this because I did it myself once. I requested close to 8 million hands that I had played on PokerStars from them.