The Punisher has mostly been a man who works alone and typically wants no help from others as he wages his war on all criminals. However, if one man earned his place as a Punisher sidekick, it's Microchip.
Microchip debuted in Punisher comics in 1987 and has appeared in two adaptations of the Punisher, both in 2008's Punisher: War Zone, portrayed by Wayne Knight, and later in the Netflix series by Ebon Moss-Bachrach. However, as important as Microchip was in Frank Castle's life, he hasn't been seen since 2011 when Punisher killed him.
Microchip's real name is David Linus Lieberman, and he grew up in Brooklyn with a knack for computers. A professor at his college blackmailed him into hacking into a bank, and when he did it, he ended up caught and almost died. He went into hiding, lost the woman he loved, who was pregnant with his child, and ended up sliding into the life of a world-renowned hacker. This was when he met the Punisher. Microchip's nephew was murdered, and he needed help. Punisher recruited him to help him in his war on criminals, and along with his now-grown son Louis, he helped Punisher every step of the way. Much of his backstory is found in the 1993 two-issue series, The Punisher: The Origin of Microchip by Mike Baron, Carl Potts, Louis Williams, Art Nichols, Josef Rubinstein, John Kalisz, and Michael Higgins.
The first comic book appearance by Microchip came in 1987 in Punisher Vol. 2 #4 by Mike Baron, Klaus Janson, and Ken Bruzenak. In this issue, Microchip was already working with Castle. He ensured Frank had all the tech he needed, mostly by designing and buying equipment and laundering the money that Punisher took from the criminals he killed to finance this. This was also where Microchip's son Louis first appeared. However, tragically, Louis died a few issues later, and Microchip dedicated his life to helping Punisher in this vindictive mission.
Sadly, the relationship between Punisher and Microchip was not destined to last. By 1994, Microchip decided Frank was growing too violent and dangerous and losing control of his sanity. He decided he needed to fix Frank or find a replacement who was not so deadly. In Punisher Vol. 2 #97 by Chuck Dixon, Rod Whigham, Rudy Nebres, Chi Wang, and Jim Nova, he locked up Castle to help restore his sanity and found a possible replacement in Carlos Cruz. However, Punisher escaped and set out to kill Microchip for attempting to replace him. Before he could, a corrupt S.H.I.E.L.D. agent named Stone Cold bombed Microchip's base, and the hacker died.
Years later, Microchip returned from the dead thanks to Parker Robbins. What resulted was one of the more disturbing storylines in Punisher comics, as Microchip wasn't the only person resurrected. Also returning was Frank Castle's family as well as Micro's son Louis. All Micro had to do to get his son back was kill G.W. Bridge, which he did. That sent Castle after him for revenge. Frank ended up re-killing his entire family by burning them to death. He also killed Louis, believing they should never have returned from the grave.
In Punisher: In the Blood #4 by Rick Remender, Roland Boschi, Dan Brown, and VC's Joe Caramagna, Jigsaw captured Punisher and Microchip and locked them together in a room. This gave Frank a chance to kill Microchip once again. Before he died, Microchip told Punisher his family had no memory of their original death. Their last memory of Frank Castle was now him murdering them and not understanding why. Punisher slit Microchip's throat, and his former ally died once again.