While he might be credited with the role here's why Toby Kebbell didn't really get to play Doctor Doom in 2015's Fantastic Four. The Fantastic Four comic has a huge fanbase but the "First Family" hasn't had much luck when it comes to live-action. Their first movie is the still unreleased Fantastic Four from 1994. This low-budget adaptation was produced by Roger Corman and was only put into production so the producer could hold on to the rights.
A big-budget version eventually followed in 2005, starring Jessica Alba and Chris Evans. The cast would also return for 2007's Fantastic Four: The Rise Of The Silver Surfer, but while both movies were financially successful they were lambasted by fans and critics alike. Josh Trank later helmed the 2015 reboot, featuring Michael B. Jordan (Creed) and Jamie Bell. This version would soon become infamous due to its troubled production, including extensive reshoots that reshaped the second half of the movie and Trank essentially disowned the released movie.
Trank's Fantastic Four was a critical and commercial bomb, and talk of a sequel quickly came to nothing. Trank championed his original, darker cut of the movie before the reshoots, which included a major action sequence with Ben Grimm (aka The Thing) that was featured heavily in the trailers but cut from the released version. Toby Kebbell (Kong: Skull Island) played Victor Von Doom in Trank's movie and would later back up the director's claim of a better cut, in addition to admitting he barely got to play the actual transformed Doctor Doom in the final version.
Kebbell's Von Doom appears to have undergone the biggest transformation from script to final cut too, with early interviews for Fantastic Four revealing the character was renamed Victor Domashev, an anti-social programmer labeled "Doom" on his blogs. This element is totally absent from the released movie, and while his name is Von Doom, this is only spoken in off-screen dialogue. Kebbell also revealed in a Daily Beast interview that after Von Doom undergoes his transformation on Planet Zero - where his spacesuit melds with his body - that's not really him playing the part.
Kebbell wasn't involved with the majority of the reshoots for Fantastic Four, so when Doom returns from Planet Zero, with the exception of three scenes, he's played by another performer. 'I played Doom in three points: Walking down a corridor, killing the doctor and getting into the time machine, and lying on the bench,' Kebbell revealed. The actor was also unhappy with certain elements this unnamed performer brought to the part, such as the limp Doom has when he's rescued. A scene depicting Doom pulling himself of rubble after he's abandoned on the planet didn't make the cut either.
It's hard to say how much better Trank's original version of Fantastic Four would have been, considering the production was said to be a mess long before reshoots occurred. It does feel like character development was sacrificed during editing, with Kebbell's Doctor Doom suffering the worst. Kebbell worked to craft a compelling villain, but re-edits and reshoots removed much of his work - including literally removing most of his performance as the transformed Doctor Doom.