What is the hardest dive in diving?

Answer 1

The hardest possible difficulty of a dive executed on a springboard is:

executed on the 3 meter platform and is 409C - in non diving terms this is an Inward 4 1/2!! which is not something i have even seen in the olympics, as its so difficult, but i am sure someone has managed it at some point

Closely following this would be a 5339D which is a reverse 1 1/2 with 4 and a half twists!

hope this helps
-Jake