Richard
It was not uncommon for medieval knights to wear some type of robe or other clothing over their armour when they were not in battle. Often they wore a tunic even in battle. The Emperor's robe is a sign of office. He had to remove his headgear in order to put on the crown. It was also convenient to remove his gauntlets, just as we remove our gloves when we go indoors in winter.
Anyhow, the Emperor is not necessarily a person. The card symbolizes the office of emperor, and the armour and clothing are symbolic of the political office as well as the responsibility to defend the realm. ETA. In this connection, see my post about The Emperor in another thread.
