Shark was a state-of-the-art crystal powered android, whom the council built in the 23rd Century as a super soldier. Shark was instructed to bring Jack Deth back to the future so Alice could give him his assignment. Shark later returned to help Jack stop Col. Muthah, and he became his full-time sidekick.
In the fourth film, Jack loses Shark to Solonoids and gives Harris a telling off for refering to his partner as "IT", granting respect to instant junk.
Shark was played by R.A. Mihailoff, who is known for appearing as Leatherface in Texas Chainsaw Massacre 3.