interveneur
Interveneur is a term, primarily used in French-speaking contexts, that refers to an individual or entity that intervenes in a situation. This intervention can take many forms and occur in various domains. In a legal context, an interveneur is a third party who joins a lawsuit or legal proceeding to protect their own interests, which may be affected by the outcome of the case. They are not one of the original parties but have a vested stake in the matter.
In a social or humanitarian context, an interveneur could be a person or organization that steps in