The 1957 version of the Star Chief was called the Star Chief Bonneville, and it was the highest performing Pontiac car at the time. The car did well enough that Pontiac decided to promote the Bonneville name to its top car in 1958. That left the Star Chief a step below, but it was still among the better-optioned cars made by Pontiac.
By 1959, the Star Chief was only sold in sedan and hardtop body styles, while the more-popular Bonneville and Catalina were given all body styles that Pontiac was making at the time. It seemed that the new cars on the block were receiving all the attention, and the Star Chief was being left behind to slowly fade away.
By the 1960's, the Star Chief name remained only as a performance version of the Catalina with better trim. They are also rarer and more desirable than the regular Catalina.
The final year of the Star Chief was 1966, when it was used alongside the Executive name. The Executive would go on to be a mid-level car in its own right the following year.
These Pontiac Star Chiefs, especially the early models, are highly collectible. You can sometimes see them listed on eBay, and you might find a good deal or two. There are also some very rare parts listings on there.