A legal guardian is a person appointed by a will or by legal terms to assume responsibility for incompetent adults or minor children. If a parent dies, this will usually be the other parent. If both die, he is often a close relative.
Separate legal guardians may be appointed for the person ("guardian of the ward") and for the estate, as a person may be competent in one area but not in the other. For example, Stella is incapacitated due to dementia: her daughter Cindy (a registered nurse by trade) may be appointed to guard Stella's person to make sure she takes her medications, while Cindy's husband Alan (a Certified Public Accountant by trade) may be appointed to guard Stella's estate so she doesn't get tricked into sending money to a scammer.