Entry into lawsuit by third party who dispite not being named party to the action has a personal stake in the outcome.
Example: Defendant damages real estate owned by 3 tenants
- 2 tenants sue the defendant to do the real estate repair.
- 3rd tenant intervenes in the lawsuit to make sure that the money is recieved to repair are actually done.
Trustee sues or is sued and the beneficiary of the account intervenes because they have an interest in the money that may get paid out of the account
If an agent is sued for wrongful act in scope of employment. Principal who is nicariously liable can intervene to make sure defense is adequate.