Insulin
The hormone that lets glucose move out of the blood and into your cells.
Insulin is made by the pancreas and acts like a key: it lets cells take up glucose from the blood for energy or storage. After a meal, insulin rises to bring blood glucose back down.
In type 1 diabetes the body makes little or none; in type 2, cells respond to it poorly (insulin resistance) and the pancreas struggles to keep up. Some people take insulin as medication to do the job their body can't.