The organ primarily responsible for hormone regulation in the body is the endocrine system, specifically the pituitary gland, often referred to as the "master gland." It produces hormones that regulate various bodily functions, such as growth, metabolism, and reproduction. Other glands like the thyroid and adrenal glands also play significant roles, but the pituitary orchestrates their activities by releasing stimulating hormones. The balance of these hormones is vital for maintaining homeostasis and overall health.