A fiduciary duty is the highest standard of care in law and finance. When someone has a fiduciary duty to you, they are legally required to act in YOUR best interest — even if it conflicts with their own personal or financial interests.
Who has fiduciary duty? Financial advisors, trustees, bank directors, lawyers, and corporate board members. For example, a bank trustee managing your inheritance must invest it wisely for your benefit — not in risky ventures that earn them higher commissions.
Breaching fiduciary duty is a serious legal matter. If your financial advisor secretly invested your retirement savings in their cousin's startup, that is a breach — and you can sue for damages. The 2008 financial crisis raised massive questions about whether banks fulfilled their fiduciary duties to clients and shareholders.