Claimant
/ˈkleɪmənt/
Definition 1 of 2
Pro Tip 1/3Legal Disputes
Often used in legal contexts where someone asserts a right or ownership. 
The claimant sought damages for the breach of contract.
Pro Tip 2/3Assertive Connotation
Implies the person is affirmative about their claim, often confident or aggressive. 
The claimant to the estate refused to compromise on his demands.
Pro Tip 3/3Ownership Claims
Specific to asserting a legal or moral right to property or inheritance. 
The claimant of the artwork was required to produce proof of ownership.