- "Look at that magnificent creature, so dangerous, so deadly. I shall name him Sleuther."
- ―Tuffnut Thorston[src]
- "After Hiccup rescued this Triple Stryke from hunters, it settled amongst the wild Dragons on Dragon's Edge."
- ―Dragons: Rise of Berk
Sleuther first appeared in the episode Stryke Out, in which he was the champion of a Dragon Fighting arena owned by the Dragon Hunters. However, fans got tired of the Triple Stryke's constant quick wins and attendance began to drop. Ryker demanded that the manager find a way to make the fights entertaining again, or else.
When Hiccup and Toothless were captured in a Dragon Hunter trap and sent to the fight ring, the manager finally found a way to boost attendance, which was to have Toothless battle the Triple Stryke. After a long battle, Toothless won and was about to kill the Triple Stryke, but noticed the pain and sadness in its eyes and allowed it to live.
It then helped Toothless, the Dragon Riders, and the other captured dragons break out of the ring and escape. However, unlike the other dragons, the Triple Stryke had been in captivity for so long, that it didn't know how to be free. However, with encouragement from Toothless, it finally left the ring. Flying back towards Toothless, the Triple Stryke revealed that it wanted to go back to Dragon's Edge with the Riders. Tuffnut named the dragon Sleuther, and they all returned to Dragon's Edge.
Despite his new freedom, Sleuther still displayed hostile behavior towards the Riders. Hiccup and Astrid attempted to train him, but he continued to attack them. They gave up their efforts so they could prepare for a storm that was approaching the island.
While searching for their dragons that were scattered by the storm, Sleuther found them and attacked again. However, Astrid had been blinded earlier, leaving her vulnerable. Hiccup, Toothless, and Stormfly managed to chase him off for a bit, but he soon returned. Despite her lack of sight, Astrid noticed the clicking sounds the Triple Stryke made during each strike. Using Stormfly's discarded spines and clicking them together, she manages to get close enough to Sleuther to establish trust.
When the Dragon Hunters attacked Dragon's Edge in their latest scheme, several of them cornered Sleuther. Dagur and Shattermaster diverted their attention, giving the Triple Stryke an opportunity to escape. However, Shattermaster had been injured in the fight. Sleuther came back to assist Dagur against the Hunters, even letting him ride on his back. Hiccup arrived and told them to take Shattermaster back to the base for treatment.
Sleuther was a very aggressive dragon in the dragon fighting arena. He was known to kill other dragons as Ryker said "if the Triple Stryke kills that Night Fury." In a fight with Toothless, Sleuther was spared by Toothless as he had won the fight. Sleuther learned from Toothless that dragons don't need to kill other dragons. Sleuther has gained a lot of trust for Toothless as he wanted to live in the Edge but he showed some uncertainty of leaving the Dragon Fighting Arena as he lived in captivity for too long, but Toothless gave him encouragement to be free. Later, being free, Sleuther gives out enjoyment of freedom by spinning and flying openly. He then sticks out his tongue like Toothless which shows that he is playful, just like Toothless.
Though he was released from the Dragon Arena thanks to the riders, he still showed hostility towards them. This is most likely due to the species' naturally aggressive nature. Even though Sleuther was with Toothless, a dragon he had formed a close bond with, he didn't show any sign of hesitation in attacking. This is likely the result of his time in captivity, where he was forced to partake many battles to the death, causing him to still be wary of humans and dragons, even those he was close to. Its also possible Sleuther was defending his territory, as its possible the riders didn't realize they trespassed the territory he made in the Edge. This could indicate that Triple Strykes are very procreative.
But after discovering Sleuther responded to clicking sounds, he appears to have calmed down, which made him more susceptible to training. He was quick to assist Dagur after the Berserker protected him, which could mean that Sleuther has made some amends with his past, as he was returning the favor to Dagur.
- For some reason, this dragon is referred to as "Slasher" in Rise of Berk.
- Sleuther was released in Rise of Berk the same day the third season of Race to the Edge aired.
- He has a personality similar to Toothless.
- Since Toothless was the one who taught him mercy and freedom to fly, Sleuther was technically trained by the Night Fury.
- The way that Sleuther closes his eye when Toothless was about to kill him is very similar to when Toothless closes his eye when Hiccup was going to kill him in the first movie.
- Even though Tuffnut named him Sleuther at the end of Stryke Out, he is referred to only as "the Triple Stryke" in Blindsided and Shell Shocked, Part 2.