Hob

 was the loyal robot servant of Josiah W. Dogbolter. (COMIC: The Moderator, Time Bomb!)

According to another account, Hob was flung into the Time Vortex after the Dogbolter Temporal Rocket exploded, and was heavily rebuilt into a gigantic, green, monstrous spider-like figure, with his head extending out of a cavernous jaw.

Hob ended up on Maruthea, where he built a database over three million years, dedicated to the life of Death's Head. He did this to track down Death's Head and force him to find his lost master, whom he faithfully swore to locate across space and time. He became enraged at and denied any suggestion Dogbolter had perished in the explosion. After viewing the database, two versions of Death's Head and Tuck incapacitated him with the help of the Seventh Doctor. (COMIC: The Incomplete Death's Head)

He still served Dogbolter by the time he became President of the Solar System and Melanie Bush delivered him the Doctor's TARDIS, who was suspicious of him. He told Mel of the consequences of reneging on her deal. He used the technology created from the Gallifreyan knowledge to wipe the Seventh Doctor, Ace, and Narvin out of time. Mel's back door into Dogbolter's system allowed her to control Hob. He told her about the Quantum Possibility Engine. He fell into the hot tub in Dogbolter's suite, and remained there until Dogbolter used it. (AUDIO: The Quantum Possibility Engine)

In anticipation of Dogbolter meeting Frobisher again, Hob was installed with a null-beam to block Frobisher's shapeshifting Whifferdill abilities. After Dogbolter was broadcast on the Galactic Broadcasting Corporation confessing to murder, Hob offered his resignation. (COMIC: The Stockbridge Showdown)

Behind the scenes
Jamie Anderson, who had to cast the character for The Quantum Possibility Engine audio, which he directed, was searching for someone who could channel Peter Lorre, the actor portraying Joel Cairo in the movie. (The Big Finish Podcast, 21 October 2018.)