Who is Stony Stevenson from The Sirens of Titan and what is their importance?

Stony Stevenson is Constant's best friend on Mars, and is one of the "real" commanders. He helps Constant try to remember what he can about his past, encouraging him to write it down so he can recall it whenever his memory is erased. Stony is found out by the other commanders and is sentenced to death for helping Constant. It is Constant himself who strangles Stony at the execution, unaware of what he is doing or who Stony is at the time.