Unlike most Indiana Jones fans, I didn't think Raiders of the Lost Ark was the best film in the series. But Marion Ravenwood was a good character for Indy's story. From what I remember she was the daughter of one of Indiana's mentors.
And they two of them had a romantic past before the movie began. But Indy apparently left her and broke her heart. According to the novel based on the movie, she was 15. Indiana Jones was almost thirty... Yikes.
But despite her protests, she helps Indiana in his quest to save the land/world from the Germans.
At the end of Raiders, they don't break up. But in the next movie, they obviously have. Go figure there.
She shows up super old in the Kingdom of the Crystal Skull. She's the mother of Mutt, a young man who had bumped into Indiana more than once.
And she surprises him with the whole "he's your son, actually, lol" line. What I don't get is that she named him Henry Jones III, which Mutt should realize that Indiana was his dad. Was Mutt really that darn dumb?
They get married at the end of the movie series. It only took Indiana until he became a senior citizen to be tied down.