A fiduciary is an individual or organization legally responsible for managing assets on behalf of someone else, usually called the beneficiary. The assets must be managed in the best interests of the beneficiary, not for the personal gain of the fiduciary.
However, the concept of acting responsibly can be broadly interpreted, and may mean preserving principal to some fiduciaries and producing reasonable growth to others.
Executors, trustees, guardians, and agents with powers of attorney are examples of individuals with fiduciary responsibility. Firms known as registered investment advisers (RIAs) are also fiduciaries.
Many so-called financial advisors have no legal obligation to have your best interests in mind.
Take stockbrokers – they may really, really want to make you $$, but they have no legal obligation to hold your interests above their own.
What you should look for? Someone who acts as a fiduciary. Here's a pretty good layout of their responsibilities.
Here’s more