Even just a few years after its release, the first game never had a lack of concept art for its characters and environments. You could always find plenty of interesting concepts in Naughty Dog's old web site, but strangely, none that concerned the gameplay. This is because they were all kept by the game's producer and main designer, David Ray Siller (commonly known as Dave Siller).
Though not a member of the Naughty Dog studio, Dave was one of the most important people to the project. As the game was being published by Universal Interactive Studios, several of their collaborators worked with Naughty Dog to make things happen. Dave was one of these people, and though he was credited as producer in the game, his integral role as the man behind the gameplay we all know and love remained ignored for almost 20 years, as did his experience during development. In fact, if you take a look at the game's credits, you won't find anyone listed as designer.
When one of the gameplay mechanics of the original game comes to your mind, it was most likely designed by Dave Siller. In fact, several of his ideas were also used in Crash Bandicoot 2 and 3, despite his work in the series being limited to the first title. Item pick-ups, abilities, level maps, and lore were just some of the few ideas proposed by Dave.
In mid-2015, Dave reached out to the public and began telling his story on Facebook, using a page he had dubbed "Crash Bandicoot Untold Story". He posted some of the concepts he had created for Crash Bandicoot and detailed his relationship with Naughty Dog and other people, along with the reasons why he had kept the whole thing under wraps for so long. The truth, it turns out, is far from the ideal view that is commonly associated with this game's development:
I was the main designer of the original game (as well as the Producer) but Jason, Andy and Cerny do not want that revealed. They wanted all of the credit as they were all insecure and extremely greedy (especially when Sony entered the picture). They have threatened me and I have kept quiet all the while having them black-ball me from getting work. I never produced a unsuccessful game, yet I still can barely get work.
Jason and Andy were, as mentioned, the co-founders of Naughty Dog, while the third person Dave refers to is none other than Mark Cerny, a prominent figure in the video game industry who had an extensive history with this franchise. However, there is a lot more to this story than a simple game of interests.
You can learn many more details about this situation and the development of the first game by reading an archive of Dave Siller's Facebook posts. Many interesting tidbits were posted, along with never-before-seen concept art and even stories from the perspective of other people, such as Craig Anthony Perkins (who did the excellent Quality Assurance for the game) and Joe Pearson (one of the main artists who came up with the original Crash Bandicoot universe and characters).