Glycogen is a polysaccharide used for energy storage by

The liver and muscles.

Explanation:

Liver and muscles store glucose, in response to insulin hormone, in a form of glycogen for use during starvation period. When glucose is too much in the blood, insulin is secreted by islets cells in the pancreas. Glycogen synthesis is then initiated in liver where it is stored.

Glycogen is a polymer of glucose just like starch in plants. 60% of glucose from glycogen store is used up by the brain as its only source of energy.