plaintiff

n. claimant, person who brings a lawsuit to court; accuser, one who charges with an offense

A plaintiff (Π in legal shorthand), also known as a claimant or complainant, is the party who initiates a lawsuit (also known as an action) before a court. By doing so, the plaintiff seeks a legal remedy, and if successful, the court will issue judgment in favor of the plaintiff and make the appropriate court order (eg. an order for damages).
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Noun
1. a person who brings an action in a court of law
(synonym) complainant
(antonym) defendant, suspect
(hypernym) litigant, litigator
(hyponym) suer, petitioner
(classification) law, jurisprudence

(n.)
One who commences a personal action or suit to obtain a remedy for an injury to his rights; -- opposed to defendant.
  

(a.)
See Plaintive.
  

The person who brings an case to court; who sues. - (read more on Plaintiff)