He was already quite famous by that time, he'd done nearly 30 movies before that.

None of which garnered anywhere near as much acclaim as Pulp Fiction did. Unless you consider Jungle Fever a cinematic masterpiece

Success isn't measured in critical acclaim. He was in many popular movies including some blockbusters like Jurrassic Park and was quite successful long before Pulp Fiction. Pulp Fiction was far more notable for reviving John Travolta's career than doing anything for Sam Jackson.

If Jackson himself measured success in the amount of supporting roles he could land, then sure he was "successful" prior to Pulp Fiction. Surely you'd agree that he didn't play in any noteworthy lead roles until AFTER Pulp Fiction...

Sure. But one doesn't have to be the lead to be successful, and this thread is about success.

makes me think about Morgan Freeman. Its pretty hard to find pictures of him young.

Try searching for images of "Morgan Freeman Electric Company".

Okay, that was weird.

(And I watched that when I was a kid, too - I don't remember much of it.)