Nowadays, its uncommon for someone to represent themselves legally, instead hiring someone dedicated to the job. Whats behind the idea of lawyers as a profession?
Disclaimer: I'm coming from a background in Speech, not in History.
As early as Classical Greece there were professionals who would help you to represent your case in front of court. Obviously the legal system was quite different, but the essential part of delivering speeches to defend yourself was still core. These weren't lawyers technically (as in professionals who understood the ins and outs of the written laws and codes). They were called logographers and today we would probably call them speechwriters instead.
Still, the idea of having someone else to aid in your representation in court at least dates back to the 4th or 5th Century B.C.
Which legal system? Which era of history? Sorry to ask followups but to give you the data you want I need to make sure I understand your question fully.