Who is a person that voluntarily joins an action with the permission of the court?

An intervenor is a person who voluntarily enters into a legal action with the permission of the court, typically because they have a personal stake in the outcome of the case that might not be adequately represented by the existing parties. This legal mechanism allows individuals or entities to assert their interests and present their arguments, contributing to the comprehensive resolution of the issues at hand. The court's permission is vital, as it ensures that all parties are notified, maintaining the fairness and integrity of the judicial process.

In contrast, the other options refer to different legal concepts. A junior mortgage pertains to a lien that is subordinate to a prior mortgage, an intestate refers to an individual who dies without a will, and joinder generally relates to the process of joining multiple parties or claims in a legal action. Each of these terms describes distinct legal situations and does not encompass the idea of voluntarily joining a legal action, which is the defining characteristic of an intervenor.