What is the major superficial muscle of shoulder?

Deltoid muscle

The deltoids are the largest and most superficial muscles of the shoulder. They are responsible for the abduction, flexion and extension of the arm. The deltoids consist of three parts, the anterior, lateral and posterior deltoids. The anterior deltoid originates from the clavicle and inserts into the humerus, the lateral deltoid originates from the acromion and inserts into the humerus, and the posterior deltoid originates from the spine of the scapula and inserts into the humerus.