Known, does not equal been ruler already. Ex-rulers are known people, but that doesn't mean that only ex-rulers are known. As to what you think Terran needs, I don't know the internal things that some pointless figurehead is really going to help out Terran. As to your second, Marco could be that person but I don't have the time to make that happen. Also Marco is more of semi-known, he knows people minorly but generally always having good relations.
Um, internal figureheads are very, very important. They set the tone for the realm. Kas did an excellent job at that for a little while... then he turned into a Glaumring-clone.