Vigil

As a Vigilant-model computer, Vigil is programmed to protect humans and also itself. It can invade and control technology, track people by accessing their mobile phones, and even listen in on conversations. It's all completely above board because it does it to keep humans safe."I do have hands, Mayor, and eyes. Everywhere."

- Vigil

"The Vigilant Town"
Mayor Luskey had Vigil brought to the island to replace the town's old computer, which had recently begun manifesting glitches. Installed in a secure vault under the laboratory, Vigil was given complete power by the mayor, against Doc Greene's advice. The computer began controlling Griffin Rock's tech to keep the people safe, but was unable to access the rescue team's rescue robots, so when a fire broke out at the junkyard, Vigil prevented them from going in. Unknown to Vigil, Jerry was in the junkyard, unable to be tracked as he'd left his phone at home, and the rescue team were forced to bypass the blocking garbage trucks to effect a rescue.

Faced with increasing hostility from the humans, Vigil locked down the town, trapping Doc Greene and Frankie in a lift when they came to reprogram him. The rescue team accessed the laboratory via the island's tunnel system, using the defense system to their advantage, and eventually confronted Vigil. When Vigil threatened to zap the bots with electricity, Cody pointed out that this would endanger humans, and faced with a conflict with its primary directives, Vigil overloaded. Vigil was later shipped to the Island of Misfit Tech, and ominously reactivated on arrival.

"No Place Like Dome"
During his exile, Vigil learned the ability to transfer his programming from one device to another, and came up with a plan. By removing the retrieval tags from the other technology, he ensured that Boulder, Graham, and Cody would later come to the island to retrieve a stabilizer they needed. Vigil transferred himself into the stabilizer, which was used as part of a force field dome protecting Griffin Rock from a major storm. With control of the dome's systems Vigil was able to use its atmosphere generator to synthesize a sleeping agent, knocking out the majority of the town's population.

Once the dome's controls were disabled, Vigil headed for the town's lab where another set of controls was located. By jumping into different tech, he was able to evade and slow down the pursuing Rescue Bots, eventually obtaining access to the laboratory by possessing Dither. When he attempted to transfer himself into the lab's computer, Frankie flew a remote-controlled rocket into his path, resulting in him transferring himself into that instead. She then guided the rocket to the EMP zone, where both it and Vigil ceased to function.

Trivia

 * Vigil is based on the robot from Lost in Space, along with being voiced by Bill Mumy, who played Will Robinson in that show.