What would spark people to attack and kill their own brutal dictators? I know that people like Mussolini, Gaddafi, Saddam and Ceausescu were dictators who were brutally slaughtered, but has history shown that the people themselves could topple and kill their dictator or would they require foreign assistance? In addition, how plausible would it be for dictators such as Assad, KJU or Putin to be killed by their own people?
To answer the first part of the headline question: it's rare for dictatorships to be overthrown through a popular rising, ie 'from below'.
Milan Svolik has done the legwork here. His Politics of Authoritarian Rule assembles some data on the exit of dictatorships from office in the post-war era. According to him, the leading causes of dictators' non-constitutional falls from power are:
As can be seen, coups are by far and away the largest single reason for the failure of dictators. Which is why pleasing their own internal power-coalitions (what Bruce Bueno de Mesquita calls their 'selectorate') is so important. The unfortunate reality is that repressive force is typically sufficient that placating the wider population, who have little stake in the political process in any case, is not a priority.
I also stressed non-constitutional above. That's because the figures omit those pre-arranged handovers of power within a dictatorship. Think of the transition between Soviet General Secretaries or the quasi-elections of PRI Mexico. The key point there is that, where robust institutional structures are in place, dictatorships can long outlive the original dictator.