A surname commonly found in ireland
Not to be confused with O'Riordan.
Riordan is a surname of Irish origin; Rearden is a variant of it. It is an Irish equivalent of the name Jordan. From ri “king” and bardan “poet”, it means “royal poet”. In Irish tradition, the poet was very highly regarded in any royal household, as he acted as scholar, historian and advisor to the king.
Riordan also from Hebrew ירדן (Yarden) means "one who descends" or "to flow down".
https://en.wikipedia.org/wiki/Riordan