The Flexor Digitorum Superficialis Muscle and the "deep finger benders" the Flexor Digitorum Profundus.
In college most physical educators whether they are pursuing an undergraduate or graduate degree very seldom learn the anatomy of the forearm and hands. It just isn't taught in most Kinesiology programs nationally.
What occurs because of this anatomical educational approach is that grip and forearm exercises take a back seat to other lifts. The very implements, 'our hands' that we utilize to play most sports with tend to be neglected.
At the end of a workout athletes are often instructed to do wrist rollers, grip a few things or maybe a "finisher" exercise such as a farmers walk.
The grip and forearm need not be the last exercise that is done in a workout. Prioritizing the grip and taking the approach that the hands and forearms are important, will dramatically change the strength of athletes.
When using a gripper do not neglect the Flexor Digitorum Profundus. These muscles are located in the forearm and have four tendons one in each of the finger tips and initiate the bending of each finger.
The Flexor Digitorum Superficialis muscle tendons also attach to the index, middle, ring and pinky fingers only to the second bone down from the finger tips.
When gripping make sure you initiate the movement with the Profundus. The Flexor Digitorum Profundus will anchor the finger tips, assist and allow the Superficialis to begin closing the hand.
Maximally develop the Profundus and Superficialis. Big 'Super Profunds' will Get you Strong.