Who is Tinhead Ned from The Last Continent: A Discworld Novel and what is their importance?

Tinhead Ned is never seen but highly praised in popular folklore, Tinhead Ned is a sheep-stealer jailed in Bugarup in the same cell as protagonist Rincewind the Wizzard years later. Rincewind learns about Tinhead Ned from the friendly warden of the jail, the night before he is to hang. Tinhead Ned repeatedly escapes from the jail and is recaptured. He leaves notes on the ceiling of his cell, however, that tell Rincewind how to escape and he successfully follows them.