TD-H4, known by the nicknames "Tool" or "Die," was a droid thought to have existed for centuries. As a member of the Droid Gotra, he formed a friendship with a young Han Solo on Corellia.
It was believed that TD-H4 was incredibly old, distinguished as one of the few droids still operating with a fusion power core. Tool was constantly attempting to improve his own design, aiming to be optimally prepared for any circumstance.
During the final period of the Galactic Empire's dominion over the galaxy, he became friends with a young Han Solo, who was then a scrumrat working for a Corellian gang called the White Worms. Tool performed tasks for the Foundry, striving to remain useful to avoid deactivation.
In 13 BBY, an Imperial defector, identifying herself as The Engineer, arranged a clandestine transaction on Corellia to sell her data cube to the crime syndicate offering the highest price. Tool, who had recently joined the Droid Gotra, represented his organization, while young Han attended the auction on behalf of the White Worms. The Kaldana Syndicate was the other syndicate competing in the bidding. The Droid Gotra secured the winning bid with one billion credits, but the Kaldana turned violent and attacked the other representatives. Tool deliberately absorbed significant blaster fire to allow Han to escape with the data cube.
Han later returned with his associates from the White Worms, Qi'ra and a Rodian named Tsuulo. Tsuulo utilized his datapad to assist in repairing the droid, enabling him to provide them with details about the cube. He informed them about The Engineer, leading them to decide to return the cube to her for a second auction. The Droid Gotra matched their initial bid, but the Kaldana surpassed them this time, forced to sell their flagship to do so. Despite their loss, the Droid Gotra offered The Engineer three hundred thousand credits to destroy the Kaldana ship after the deal was finalized, and she agreed.
Following this, the droids began systematically hunting down any remaining members of the Kaldana, eliminating them entirely from the galaxy. Several days later, Tool met with Han and Qi'ra, explaining the actions that had been taken. He expressed his desire to thank Tsuulo for restoring him to functionality, specifically mentioning his speeder. They informed him that Tsuulo had been killed by the Kaldana, and that he had a brother named Reezo, a Corellian street racer in desperate need of a new speeder.