April 23 (Reuters) - MetLife Inc, the largest life insurer in the United States, will pay $500 million to settle a multi-state investigation into claims payment practices, the office of California's state controller said on Monday.

The investigation related to the use of the Social Security "Death Master" file, which lists those who have recently died. A number of states have accused insurers of using the list to stop making annuity payments to dead customers, but at the same time not using the list to check whether any life insurance policy holders had passed away.