The story behind the coin
In June 1886, Bavaria lost two kings in four days. Ludwig II — the "fairy-tale king" of Neuschwanstein — was deposed by his ministers on 10 June and found dead in the Starnberger See on 13 June. The crown passed that same day to his younger brother Otto.
Otto had been living under medical supervision at Fürstenried Palace outside Munich since 1883, severely mentally ill. He never governed for a single day. His uncle Luitpold ruled as Prince Regent until his own death in 1912; Luitpold's son Ludwig then took over the regency.
But a coin is a legal document as much as a piece of metal. Bavaria was a kingdom inside the German Empire, and the empire's bargain was that each state kept its own monarch's head on the coinage while sharing one currency. So the silver 5 Mark struck at Munich carried OTTO KOENIG VON BAYERN and a left-facing bust — the obverse, the heads side — for the whole of a reign that only ever existed on paper.
It ended by constitutional trick. In November 1913 the Bavarian constitution was amended so that a regency lasting ten years with no prospect of recovery could be converted into a full reign. The day after the amendment passed, Prince Regent Ludwig deposed his cousin and took the throne as Ludwig III. That is why the 5 Mark Otto stops in 1913. Otto himself lived on quietly at Fürstenried until 1916, still styled king by courtesy, and almost certainly unaware that any of it had happened.

