What type of rider was included by the policyholder who paid $10,000 for a Whole Life policy and received $10,500 after their death?

The scenario describes a situation where the policyholder paid $10,000 for a Whole Life policy and upon their death, their beneficiaries received a payout of $10,500. This indicates that the policy included a rider that not only provides the death benefit but also ensures that some amount greater than the premiums paid was returned to the beneficiaries.

The return of premium rider is designed specifically to refund the premiums paid into the policy if the insured dies, thereby fulfilling the condition of returning more than the premiums directly from the policy. In this case, the additional amount received ($10,500) can be interpreted as partly reflecting this rider's function.

In contrast, the other options do not suit this scenario. A waiver of premium rider typically allows for the premium payments to be waived if the insured becomes disabled, without impacting the payout directly. An accidental death rider provides an additional benefit specifically if the death occurs due to an accident, which does not explain the payout based solely on the premiums paid. Lastly, a supplemental income rider is designed to provide an additional income stream following the death of the policyholder but does not relate to the return of premiums.

For this reason, the return of premium rider is the most fitting explanation for the circumstances outlined in the question.