Often times an elderly or infirm person signs a power of attorney, which authorizes another person to write checks, handle finances, and sign documents on behalf of the elderly person. 

A person who holds a power of attorney is a fiduciary, having the highest duty of good faith and honesty in dealing with the elderly person.  A person holding a power of attorney is only supposed to take actions that are in the best interest of the principal.

However, sometimes a holder of a power of attorney uses the power to misappropriate the principals money or other property to themselves.  Often times this is not discovered until after the principal dies.  In those situations, the personal representative of the estate may sue the person who held the power of attorney.