Mohammad or Newton certainly.Muhammad one must acknowledge was more influential than christ.Christianity's success came after his death and owed much to his disciples and constantine adopting it.Muhammad laid down the foundations of his success himself,so i agree.I'm not saying greatest,smartest,most powerful but on influential i agree.
The only real competitors except christ are 2 others - First isaac newton.This man changed science inside out.His inventions on every single field are just groundbeaking.Physics was newton,far more influential than einstein.There's a reason Pope wrote in his epitaph -
''Nature and nature's laws hid in night;
God said let newton be,and all was light.''
Another serious competitor and i mean probably even more than newton would be karl marx.This guy is highly controversial and the communist experiment didn't exactly work out.However his observations of capitalist industrialism,the trends of human economic development and mode of production in pastoral,feudal and industrialized societies plus the causes of social inequality are proving more right every day,he also was one of the founders of modern social science,minimum wages etc.As science advances rapidly and religion's future is increasingly uncertain with atheism and materialism expanding in a 100-200 yrs one may have to say he is the one.His writings are very relevant today and is likely to remain so for a long time to come as globalized corporations now control the world economy.Like him,hate him u have to acknowledge him.
BBC News | World | Marx the millennium's 'greatest thinker'
Won a vote in britain of all places,not a place that likes communism.
The final candidate i can think of is darwin.His theory of evolution simply turned the world upside down and gave science its answer versus creationism theory.Completely changed human history evaluation and how man looked at the past.On the negative side his motto 'survival of the fittest' was misused by many dictators/imperialists in the defence of colonialism/racism/lebensraum in the east etc that led to massive numbers of human deaths and suffering.So influence was both positive and negative,but influence nonetheless.He too is thus very influential in the larger scheme of things.
On fire i agree,but i don't think it was one person as such.I think many of the ape-men discovered it seperately in different places -perhaps seperated by years but eventually.