The "Unspeakable One" or the Self-Loathing Beast (also jokingly called Rimmer's Lust Monster in reference to another entirely different context) is the physical manifestation of Arnold Rimmer's self loathing, given physical form by Rimmer's presence on the Psi Moon in the Series V episode "Terrorform".
He had Rimmer captured (who as a side-effect of the Psi Moon had a physical form while he was there) by his Hooded Hoards for the sole purpose of torturing him, part of which involved electricity (which is why the Handmaidens had Rimmer oiled, to increased his conductivity), until he lost all hope. The beast seemed resistant to bazookoid fire, but he was weak against words that appealed to what positive traits Rimmer had left, such as when Lister and Kryten told Rimmer that they wouldn't desert him. The creature also referred to Rimmer as "The Despicable One" at one point.
Behind the scenes[]

"Nightmare Norman" looms over Starbug in the sky of the Psi-moon
- Excised model shots from the episode show the Unspeakable One looming over Starbug as the ship is stuck in the swamp. These model shots can be seen in the models and FX section on the Series V DVD.
- The propmakers worked for weeks on the puppet used to represent the beast, before the director Juliet May decided to show only brief glimpses of the puppet, influenced by the movie Alien in which the creature is barely seen. More of the model can be seen, along with more of it's torture instruments, can be seen in the deleted scenes in the Series V DVD. These torture instruments include the "Mexican algarve cactus"-shaped instrument that Rimmer says his bottom was threatened with, although the "phallic instrument" is completely left out.
- The voice of the Unspeakable One was provided by Chris Barrie in a suitably villainous tone.
- In the Series XII episode "Timewave", the crew face a variation on the Unspeakable One in the manifestation of Rimmer's Inner Critic, a bald duplicate of Rimmer with a distinctive scar who criticizes all of Rimmer's actions; the only true difference is that the Critic perceives himself as 'helping' Rimmer by reminding him of his limitations.