Consequently, every application to the court on behalf of a minor, a mentally incapacitated person, or a person detained without access to an attorney, who does not have a legal guardian or someone authorized to act on his or her behalf with a power of attorney, must be made through a next friend (prochein ami, prochein amy, or proximus amicus).
In the case of mental incapacity, a conservator, guardian, or committee represents the person in court.
In United States law, next friends have sometimes been permitted to litigate habeas corpus actions to challenge the detention of prisoners who are not able to appear in court on their own behalf.
For example, family members, attorneys, and non-governmental organizations have sought to bring claims as next friends on behalf of detainees classified as enemy combatants at Guantanamo Bay and elsewhere, during the War on Terror following the September 11, 2001 attacks.
[3] Another case arose following the monkey selfie affair, when the animal rights organization People for Ethical Treatment of Animals sued photographer David Slater, asserting itself as the next friend of a Celebes crested macaque.