Susan.

In some ways the least developed character of C.S Lewis's four Pevensie children in the Narnia Chronicles, in 'The Last Battle 'Clive Staples uses Susan to demonstrate a major Christian point.
She has experienced all the things which the other three have; she has seen and been involved in 'miracles' and yet as she grows older, she has been distracted into a shallow, superficial and trivial lifestyle.
'The Last Battle' sees most major characters arrive in what is portrayed as Heaven - but Susan is missing.
Will she eventually make it? - We are not told!
Certainly, Lewis uses Susan as a stark warning to Christians that they must not allow their attention to be diverted from the Cross.