Due to Spook's POV's in HoA, there has been some confusion about what exactly a savant is.
It is generally accepted that an Allomantic savant is someone who has burned a metal for a long period of time, warping their soul and giving them increased power from that metal.
However, there is some issue about the implied dependence of the savant on their metal. In HoA, Spook says that without tin, he seems blind, deaf. However, he also says something along the lines of "this was how normal people sensed the world."
Spook only was dependent on tin because he was used to the sensations, painful though it was.
There are likely more savants than Spook in Mistborn. Clubs may have been, Breeze almost certainly was, and Marsh was almost said outright as a savant.
Waxillium Ladrian is a steel savant. His 'steel bubble' is something that few Coinshots have been able to do. I believe that there is a WoB confirming as much, but I don't know where it is.
A savant does not have dependence on their metal, only increased precision and strength in it.