In order to purchase life insurance on somebody else, you'll need an Insurable Interest in that person, and they may be required to sign the application for life insurance coverage.
Insurable Interest means you either rely on the person for financial support, or you would lose out financially should the person die.
There usually exists insurable interest between spouses, parents and their children, siblings, life partners, and business partners, among others.
Learn more about whether or not you can buy a life insurance on anyone.