As its name implies, a trust depends on trusting someone. A trustee is someone with an enormous amount of power over assets that are supposed to be managed on behalf of the beneficiaries. This is a big responsibility, and it can be a terrible problem if the trustee acts negligently.
A trust is a way of dividing ownership of property. The trustee takes possession of the property and manages it for the benefit of the beneficiaries. People sometimes set up testamentary trusts that go into effect upon their death, but it is also quite common to form a living trust.