Question

What is puppet emperor

Answer 1

A puppet Emperor is one who is assigned by external forces on throne. 
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The powers are shown to be his, but the main power lies with political or military group.
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He/She never takes a decision and the behind the curtain person or group takes all the decision and shows that the monarch is taking the decision.
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Answer 2

Puppet emperor or puppet ruler refers to a person who holds political power but in actual he is governed and controlled by outer forces.
The best example is of Battle of Plassey, one of Siraj al-Daula's general helped the British to kill Siraj al -Daula.

After his death, that general became the ruler, but he was a puppet ruler as he was controlled by British.