In the original, Roman sense of the word, a dictator was a Consul who had been granted emergency powers to deal with a time of crisis (typically war). Today, the term is associated with an authoritarian, personality-driven style of leadership.
My question is less about that transition and more about the perception of the word itself. At what point did the term "dictator" become pejorative? And why did this change occur?
More specific to my area of interest, would it be considered an insult in during WW1? Would citizens in nations that passed legislation like the War Measures Act consider that dictatorial, in the Classical sense?
The dictator wasn't a consul, although he was usually consular. The Republican dictator was an extraordinary magistracy, it had nothing to do with the consulship. Already by the late Republic the office had taken on a negative aspect. In part because of opposition by the senatorial class against an extraordinary magistracy that was increasingly becoming unnecessary and bizarre in the face of the new rights gained in the Conflict of the Orders. The dictatorship lapsed following the Punic Wars, and already in the third century there were motions proposed to limit the dictator's power, notably by suggesting the revision of the office as a collegiate one. The dictatorship was revived by Sulla, whose rule was less than affectionately called dominatio Sullae by Tacitus. And of course the Romans' memory of Caesar's dictatorship was ambivalent at best