Tank (Lilo & Stitch)

 Tank, A.K.A. Experiment 586, is an illegal genetic experiment created by Jumba Jookiba. He is designed to eat metal and grow exponentially larger with all that he consumes. He was captured by Gantu, but was rescued in "Snafu". His one true place is eating scrap metal at a junkyard. Tank is voiced by Frank Welker.

Lilo & Stitch: The Series
Experiment 586 was the 586th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to consume metal and grow exponentially bigger with each feast. 586 and the other first 624 experiments were deactivated and smuggled to Earth by Jumba during his mission to capture Experiment 626.

All of the experiment pods were released and scattered across the island of Kauai, with 586's pod landing in a car's grille.

When the car was being washed, 586's pod got wet, activating him. 586, named Tank, then ate the driver's automobile and proceeded to eat metal throughout town, including a huge factory that was being shown to some tourists, until he grew to a large enough size to go on a rampage.

Gantu had been informed about the experiment and realized he couldn't possibly catch it in a containment orb, due to how large it had grown. He then took off in his ship to chase down and capture Tank somehow.

Meanwhile, Lilo won tickets to the Elizabethan Fair and invited the hula girls (who ditched Mertle when she refused to participate with Lilo), but neglected Stitch when he told her an experiment was on the loose. Later, Stitch (who couldn't attend the fair because no "dogs" were admitted) teamed up with a lonely Mertle in hopes of stopping Tank.

However, due to his enormous size, Tank proved quite impossible for Stitch to defeat, despite his best efforts. When Gantu later attempted to capture Tank, the former was thwarted by Lilo, who brought down his ship and impeded his progress.

Tank's rampage continued to spread, where, after an attack on Stitch, he was abducted by Gantu using a tractor beam from his hovercraft. However, Lilo had requested Gantu to get Tank away from Stitch, since the latter appeared to be outmatched.

Additionally, Mertle broke off her temporary friendship with Stitch when the hula girls decided to take her back, and Lilo apologized to Stitch for neglecting him.

Tank reappeared in "Snafu", and was freed along with Gantu's other captive experiments by Lilo, Stitch, and several other experiments in a rescue mission.

Leroy & Stitch
The first 624 experiments, including Tank, were rounded up by Leroy and taken to a stadium to be destroyed. However, Lilo, Stitch, Jumba, Pleakley, Reuben and Gantu arrived before the experiments could be destroyed.

Tank participated in the following battle between the experiments and the Leroy clones by eating attacking Leroys.

However, the Leroys soon gained the upper hand in the battle, but were defeated when Lilo, Stitch, Reuben and several other experiments performed the song "Aloha `Oe," which caused the Leroy army to shut down due to the original Leroy's fail-safe.

Trivia

 * Tank has shrunk from a massive size back to his normal size between "Tank" and "Snafu", suggesting that he returns to his normal size after a while without eating any metal.
 * Tank's pod color is blue.
 * Tank is described by the experiment computer screen as, "Experiment 586 Primary function: Metal consumption. The experiment becomes bigger with everything it eats."
 * Tank appears in the game Lilo & Stitch: Alien Interception along with Plasmoid, Dupe, Clyde, Yang and Hämsterviel.