Chymotrypsin.

Many digestive enzymes are synthesized as zymogens. A zymogen is an inactive precursor of an enzyme (look at the word). Pepsinogen, trypsinogen, and chymotrypsinogen are all examples of zymogens in the digestive system. H⁺ activates pepsin. Enterokinase activates trypsin. Trypsin activates chymotrypsin.