Dmitri Mendeleev was a Russian chemist in the 1800s who is most famous for his work on developing the periodic table of elements. He discovered that there was a regularity to the known elements by arranging them in order of their atomic weights.
Mendeleev was also able to predict new elements that would be discovered and what their properties would be by noticing gaps in his periodic table. Three of the elements he predicted, gallium, scandium and germanium, were discovered in his lifetime, thus providing strong support for the accuracy of his work.
Element number 101 of the periodic table, the radioactive mendelevium, is named after Mendeleev. There is a also a crater on the Moon named in his honor.