Zero! Can you imagine Math without zero? Before the zero, Mathematics would have been considered so difficult.
About 3000 years ago the babylonians mathematics had a very complicated numerical system, where they used a space between sexagesimal numerals.
The Mesoamerican that inhabited Mexico and Central America used the Zero as a separator in its 20 numeral system.
The Greeks for relegious resasons could not admit that nothing could be symboled by a symbol.
The first people that used the zero in the counting system were the Indians in the forth century BC. Then came Brahmagupta (598-668 AD), an Indian astronomer and mathematician. He was the first to use the zero and put the rules that allow using zero.
The Arabs transferred the zero from India as they transferred the spices and other trades. Mohammed ibn-Musa al-Khowarizmi (780-850 AD) a Persian mathematician, astronomer and geographer, he was living in Baghdad when the Arab traders transferred the zero in the year 773 AD. He was the first mathematician that used the “sefr” in solving the equations that equaled zero (algebra as we know nowadays), sefr was later translated to zero.
When the Arabs conquered Spain, the zero reached Europe. Leonardo Pisano Bigollo (Fibonacci) (1170-1250), an Italian mathematician, continued the work of Al-Khowarizmi with algorithms, but still the sefr or zero was not yet used.
Till Rene Descartes (1596-1650) , he made the Cartesian coordinate system depending on the point (0,0).
The last and most imporatant step was by the Sir Isaac Newton (1642-1727) and Gottfried Wilhelm Leibniz (1646-1716) as they reached calculus.