Jak is the main protagonist and titular player character of the jak and daxter series, accompanied by his sidekick, daxter. He is a human male with green-blond hair, cerulean blue eyes, and fair skin. Jak enzymes are part of the jak/stat pathway.

Some jak inhibitors are used to treat cancer. They are a type of targeted therapy. Also called janus kinase inhibitor. Recently, janus kinase inhibitors (jaki) have been developed to block the effect of proinflammatory cytokines in imids.