A trustee is someone who holds and manages property for the benefit of someone else.  When the creators of a trust die, their successor trustee takes over the tasks of managing the trust assets and carrying out the instructions in the trust documents to ultimately transfer the trust property to the trust beneficiaries.  If the trustee and the executor are not the same person, the trustee will work with the executor on trust-related tasks. 

A trustee can do many of the initial tasks and day-to-day management without the help of professionals. Other tasks, such as filing tax returns, transferring ownership of real estate, funding sub-trusts, and making investment decisions may be best handled with the help of experienced professionals, such as attorneys, accountants, and financial advisors.