What is the role of a guardian ad litem?

The function of a guardian ad litem is so similar to that of a special guardian that many of the rules governing the one would apply to the other. In Moore v. Flagg (137 App. Div. 338) the question arose as to the status of a guardian ad litem, and the court therein said (p. 346): "The plaintiff in the case at bar is William J. Moore. The cause of action set up in the complaint is vested in him. To be sure he appears by his guardian ad litem, but so does an infant in an action brought to assert the infant's rights. The demurrer was sustained upon the ground that the plaintiff had no legal capacity to sue. `A guardian ad litem is not a party to the suit, but is an officer appointed by a court of justice in a cause to prosecute or defend for, or otherwise to represent and look after the interests of an infant or an insane person whose property rights are affected by the judgment or decree, the rendition of which is contemplated.'"