Theo Otto TSX
Theo and Otto
  • Number: 1 (Theo) & 2 (Otto)
  • Class: HL Standard 14" Saddle Tank
  • Designer: Hawthorn Leslie
  • Build date: 1893
  • Ages: 83
  • Configuration: 0-4-0ST
  • Arrived on the DR: 1893

Theodore and Otthaniel, better known as Theo and Otto, are a pair of tank engine twins who live on the Dark Railway.


In 1893, Lord Theodore Dark knew he required motive power to run on the then under construction Dark Railway between its then termini at Axley, Soma, and Walschurch. He ordered two tank engines from Hawthorn Leslie & Company of Tyneside, and these arrived on the railway later that year. The two engines were named after Lord Dark and his son, Otthaniel Dark.

On the opening day of the DR, Theo and Otto, as they eventually became known, were tasked with hauling the first train. Unfortunately, the two engines were severely under-powered, and they failed climbing the gradient. They were soon repaired, but now confined to the Soma Quarry.

Throughout their early life, the twins referred to themselves as "One" and "Two", but soon grew tired of this and, after a chat with a young Otto Dark, named themselves "Theo" and "Otto". Lord Dark honoured this officially in 1938 by giving them nameplates Bearing these names.

Over the years, the twins became interested in advancing certain aspects of railway technology. Deciding that the railways needed a way of transporting goods and passengers without anybody complaining, so they set to work on constructing a teleportation device which would move them in seconds. While construction was going on, they hosted many parties on the DR, such as their cousin Sir Edgar Woolwinder's 61st birthday party. These would often involve alcohol and would end in the twins becoming incredibly drunk. The two eventually approached Dave, Brian, and Raymond to collect some materials for their teleporter, paying them with alcohol when they returned.

In 1963, the twins' teleporter was nearly complete, and they tested it on Brian's irritating visiting brother, Brain with success. However, they also made the decision to experiment with sending goods back in time, so they installed a time manipulating module to their machine. Unfortunately, this backfired severely at the machine's unveiling, sending themselves, Dave, Brian, and Raymond back in time to 1953 on the Settle and Carlisle Railway. The twins set to work rebuilding the machine, sending the other three to look for supplies and enlisting the help of a small shunter named Hunter to help them find the rarer items needed. Unfortunately, the items were stolen from the yard where two loan sharks, Victor and Ludo, lived, and since Hunter was already on their radar, they tracked them down and captured them, knocking Theo out and threatening to turn them into teaspoons. Fortunately, the machine at this point was already repaired, and with the help of the others, they managed to escape and defeat the loan sharks using the machine. Once everything was sorted, the machine was used to return to their normal time and the Dark Railway.

In 1965, the twins and the friend that they helped save from scrap, Leno, were the first to be captured by Leanne who was seeking revenge against the railway for leaving her in a scrapyard. They were quickly rescued, however. In 1967, the twins were sent away for overhaul, having not had one since 1950. They returned later that year, briefly repainted green before returning to their normal liveries. In 1969, the twins were once again repainted back into green. Later that year, they offered to carry out a blood test to determine what had been involved in an incident involving Repulse, but were held up by their equipment going missing along with some dynamite. A few days later, a fire at the Junction killed ColinCammer, and Owen, upsetting the twins greatly. After finding their missing equipment, they discovered that Repulse had killed a human, and that she stole their equipment to slow them down, as well as the dynamite to burn down the shed. When it was revealed that Repulse was actually posessed by Leanne's spirit, Otto pulled their Tau Cannon on her, and when Repulse begged him to kill her, he nearly complied. When Pogo asked Otto to use the cannon on Leanne's ghost, Otto fired, screaming it was vengeance for Owen, which allowed Leanne to finally be claimed by Pogo.

In 1971, the twins attempted to threaten Five with the Tau Cannon to try and get him to tell them about the new developments at Galen Junction. After being caught by Mr. Dark and brought up to speed on the situation, he decided to split them up for a while as punishment, choosing Theo to go into the new Galen Junction Railway Museum. To Theo's disappointment, he was placed at the back of the museum, though he later helped to tell visitors the story of the DR. After Theo started striking up conversations with Mr. Dark's son, Zeke Dark, he arranged for Theo to be moved to the front of the museum to allow him to talk wth Otto again. Eventually, Theo was let out while Otto went into the museum. When Buzz arrived on the railway, Theo was left infuriated when his batteries ran out of electricity for two days in a row, as he would require the rest of the day to recharge. The twins were upset to learn of Mr. Dark's retirement.

Now both consigned to the museum, they were met with further dismay upon learning that their home at Soma had lost its rail link due to the collapse of the viaduct leading there, and were furious with Mr. Chairman for allowing the incident to occur with his poor judgement. Clyde approached them asking for help keeping his presence hidden while still allowing him to work on the railway, and the pair debated a possible solution that they mentioned would take some time to achieve. When Zeke expressed concern about the future of Soma with the closure of the quarry, the twins suggested he turn it into a mining museum, and agreed to use their Tau Cannon to rebuild the viaduct in exchange for being returned to service. After sticking to their promise, the twins decided to use the Cannon on Clyde and alter his appearance. In their haste to complete the process they overcharged the gun, causing it to destroy itself as it fired on Clyde, leaving him with an ability to shapeshift at will and the twins no way of fixing the issue. After Dave was abducted by a demon, the twins were brought into Pogo's Locker, where they were informed of what had transpired. Pogo later gave the twins a way to contact him if they needed his help again, but the twins assured him that they were now done with science altogether.


Theo and Otto are both rather mad, but fun loving and exciteable. Theo is the cheekier of the two, while Otto is the more intelligent of the two.


Theo and Otto have both worn similar liveries throughout their lives. Upon delivery from Hawthorn Leslie in 1893, the engines were both painted light blue. Eventually, this was changed to lined black, with Theo being given red lining, and Otto being given white lining. During the 1960's, the pair wore different variations of Dark Railway Lined Green.

Upon Zeke's introduction as the railway's manager in 1973, both twins have once again been repainted. Both engines now sport Dark Railway Black, with blue and white lining. The main differences are that Theo carries the full 'Dark Railway' branding, whilst Otto wears the shortened 'DR' logo.


Theo and Otto are based on a Hawthorn Leslie 0-4-0ST named Henry, which is currently preserved and on static display at Barrow Hill Roundhouse in Sheffield.


The Dark Railway SeriesEdit





  • With the exception of Event Horizon, Theo and Otto were never seen apart in the series until series 7.
  • When depicted with faces by Dark DJ, Theo has a beard while Otto has a goatee.
  • Theo and Otto are the longest serving engines on the railway, but are not the oldest residents. That honour goes to Leno, who is three years older than the twins, but only arrived in 1965.
  • Although Dave is the main character, and was the first character to be seen in the series (along with Raymond), Theo and Otto were the first true characters conceptualized for the series.
  • According to Dark DJ, Otto is approximately 20 minutes younger than Theo.
Locomotives of The Dark Railway
Current locomotives
Theo and Otto257 SquadronSir Eustace MissendenDaveBrianEddieLenoAbominationHannahEdSidCaracus SmashBarryDe la TripColossusGooseClyde
RyanRaymondAllanTurboMr. BWarriorAndy
Former locomotives
CheapsideDark Railway No 1202JamesColinRepulseFive
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