Why hypothalamus is known controlling unit over endocrine system?

Hypothalamus is truly known as control unit for endocrine system because it mediates the information between the brain and endocrine system, meaning that when brain is required to do certain hormonal function it relays the information to the hypothalamus which in turn release some releasing hormones which activates the major hormone system (Pituitary system).

So therefore pituitary system which makes the hormones is controlled by the hypothalamus as it is messenger between the autonomic nervous system and pituitary system.