The Star Wars universe is full of surprises as triumph and tragedy could come at any moment. The best example of this came primarily during the Clone Wars, which Chancellor Palpatine orchestrated. With Palpatine in control, it meant that much of what came to pass during the Empire's reign was workshopped during the Clone Wars, including the creation of future Sith Inquisitors.
Sith Inquisitors were prominent during the Empire and were skilled hunters who used their abilities and skills with the dark side to hunt Jedi. While they weren't full-blown Sith, they could still be deadly to even the most skilled Jedi. Interestingly, it's possible the Inquisitors wouldn't have existed had it not been for the dark turn by Jedi Master Pong Krell.
Pong Krell's Choices Were Like an Inquisitor's
During the war, Palpatine tried, in secret, to create Inquisitors by kidnapping young Force-sensitive children and training them on Mustafar to do his bidding as spies. Thankfully, this plan was thwarted by Anakin Skywalker and his Clone battalion. Eventually, Palpatine found a new avenue by which to build his Inquisitorius and, following Order 66, he manipulated and tortured surviving Jedi to join the dark side. By forcing them to turn, they embraced their anger with the Jedi Order and became Inquisitors. But it's possible that the signs were written on the wall way back in the Clone Wars based on Pong Krell's actions.
Krell was a skilled Jedi and warrior and, up until his time on the planet Umbara, was on the side of the Republic. As a general, it's possible that the battles he fought pushed his darker feelings to the top, and he turned to the dark side. Then, he witnessed the fate of the Jedi, which forced him to turn on his allies. After betraying the Clones, he then sought apprenticeship before Count Dooku and fully embraced his place on the dark side. The choices he made while seduced by the dark side may have inspired Palpatine.
Pong Krell Was the Perfect Template for Future Inquisitors
With Palpatine knowledgeable of Krell's actions, it's possible he saw the potential in fostering the anger of Jedi who were fed up with the Clone Wars. Fighting a battle that went against their code was the perfect foundation to forge anger and resentment. As a result, Krell's actions and ruthlessness were more than enough to prove to Palpatine that Inquisitors were a viable option for the Empire. But aside from creating Inquisitors, there was a key factor that was perfect to execute Palpatine's plan -- loyalty.
Krell's attempt to gain an apprenticeship from Dooku wasn't the first time that the Sith Lord was presented with an apprentice. While this was forbidden thanks to the Rule of Two, Inquisitors side-lined this rule by never becoming complete Sith Lords. Instead, they were dark side practitioners who fought for the Emperor but lacked a definitive master. By allowing Krell to operate as a dark side follower but never letting him be an apprentice, coupled with seeing his desire to be one, Palpatine had the perfect template for the Inquisitorius.