Who is the person who starts a lawsuit?

Answer 1

In a tort, breach of contract, or other civil case, the person(s) or entity(ies) commencing the lawsuit is/are the Plaintiff(s). This is the party who claims to have sustained money damages as a result of the actions or inactions of the party(ies) being sued (called the Defendant(s)). The Plaintiff has the burden of proof on all elements of the cause of action, including proving the quantum of damages.

In other types of civil actions, such as that for dissolution of marriage or other equitable cause of action, the person who commences the lawsuit may be referred to as the Petitioner.

Criminal cases are different, in that they are commenced by a government entity. While the person on the receiving end of the charges is usually called the Defendant, the government entity usually brings the action in its own name (rather than being called "Plaintiff").

Answer 2

Please clarify what you mean by "start the trial."

The trial judge starts the trial in the sense that he/she initiates the proceedings from the very beginning. Nothing happens in a trial until the trial judge comes onto the bench, announces the name of the case and authorizes the attorneys or the pro se parties to give their appearances.

The prosecutor in a criminal matter or plaintiffs attorney (or pro se plaintiff) begins the trial in the sense that he/she makes the first opening statement and later gets to prove his/her case before the accused or defendant has to proceed.