Noun
guardian ad litem (plural guardians ad litem)
An individual (often a lawyer) appointed to represent the best interests of a child or incapacitated person for the purpose of a legal procedure.
A former cop turned guardian ad litem is the girl’s only advocate when Dad kidnaps them and tries to disappear. Source: Internet
“A person whose sole concern is, what is in the best interest of a child — a parent or a guardian ad litem — that role is desperately needed now.” Source: Internet
That was in my role as a guardian ad litem in South Carolina family court. Source: Internet