Explain the most important function of the trial judge in a legal proceeding?

There is no one most important function because the trial judge determines issues of both fact and law, and those decisions of the trial judge are rarely overturned by appellate courts. For example, an issue of fact might be when a trial judge must determine which witness to believe when witnesses testimony about the same event differ. Whereas, an issue of law might be when a trial judge must determine whether a law is unconstitutional.

Additionally, trial judges may sit as the ultimate fact-finder in place of a jury, so, some may say that at that time that is the most important function. Last, all of the above functions may take place in both civil and criminal proceedings.