In a jury trial between plaintiff X and defendant Y, three individuals (excluding the defendant) who can participate in voir dire are the plaintiff's lawyer, the defendant's lawyer, and the judge.
In a criminal trial where the government is the plaintiff, the prosecutor, the defendant's lawyer (or defense lawyer), and the judge can participate in voir dire.
Note that depending on the jurisdiction—and even among individual judges within the same jurisdiction, e.g., a United States District Judge in a federal judicial district—the judge may elect to conduct voir dire him/herself.