Glucagon
The hormone that raises blood glucose: insulin's counterpart from the pancreas.
Glucagon is released by the pancreas when glucose drops, signaling the liver to release stored glucose and raise blood sugar. It works in balance with insulin, which lowers it; together they keep glucose in a safe range between meals and overnight.
An injectable form of glucagon is also the emergency treatment for severe hypoglycemia, when someone can't safely eat or drink to bring their glucose back up.