Clemens Alexander Winkler (December 26, 1838 – October 8, 1904) was a German chemist who discovered the element germanium in 1886, solidifying Dmitri Mendeleev's theory of periodicity.

When Winkler subsequently analyzed the mineral, he found that the individual components only added up to about 93–94% of its total mass, leading him to suspect that a new and previously unknown element must be present.

After additional chemical purification steps over several months, Winkler isolated the pure element, germanium, on February 6, 1886 and published his results.

As no reaction occurred for him, Winkler incorrectly concluded that SiO does not exist, even though it was reported to have formed from the reduction of silica with charcoal three years earlier by C. F. Maybery.

However, Henry Noel Potter, a Westinghouse engineer, repeated Winkler's experiment fifteen years later with an electric furnace, which enabled him to increase the reaction temperature by several hundred degrees and observe the generation of SiO.