Step 1: Identify the regulators of blood sugar.
Blood glucose level in humans is mainly controlled by two pancreatic hormones, insulin and glucagon, which act in opposite directions.
Step 2: Recall the action of insulin.
Insulin lowers blood glucose by helping cells take up glucose and by storing it as glycogen, so it cannot be the answer for raising sugar.
Step 3: Recall the action of glucagon.
Glucagon does the opposite. It breaks down stored glycogen in the liver into glucose (glycogenolysis), releasing glucose into the blood and raising the level.
Step 4: Consider epinephrine.
Epinephrine can raise blood sugar briefly during stress, but it is not the principal day to day hormone for this role.
Step 5: Consider estrogen.
Estrogen governs female reproductive functions and has no main role in glucose control, so it is ruled out.
Step 6: Conclude.
The hormone that mainly increases blood glucose is glucagon, option 2.
\[ \boxed{\text{Glucagon}} \]