Step 1: What is burden of proof?
The burden of proof is the legal obligation on a party to prove their claims in court.
Step 2: Who bears it in civil cases?
In a civil case, the party who initiates the lawsuit and makes allegations must substantiate those allegations. That party is the plaintiff.
Step 3: Standard applied.
The plaintiff must prove their case on the balance of probabilities (i.e., more likely than not). The judge does not prove; witnesses give testimony; the defendant's advocate defends.
\[ \boxed{\text{the plaintiff}} \]