A power of attorney (POA) is a legal document that gives someone the legal power to act on someone else’s behalf. The person who’s been granted the authority is called the agent. The person who signs a POA, making someone else their agent, is called the principal. A POA can only be authorized by someone who’s found to be mentally competent, which is why it’s so important for individuals diagnosed with dementia to create a POA before the condition progresses.