Trustees are very similar to Executors. They are often instructed with looking after an amount of money or a property within a trust to protect the asset and its beneficiaries.
The Trustees are given powers to make sure that the Beneficiaries best interests are taken care of. They are not allowed to use the property or money they are entrusted to look after for their own gain.
It is common practice for the Executors of the Will to be Trustees.