The third kingdom “Protista” was proposed in 1866 by?

✅ Explanation: Ernst Haeckel, a German biologist and naturalist, proposed the third kingdom "Protista" in 1866. This kingdom was created to accommodate microorganisms that did not fit neatly into the existing plant and animal kingdoms. Haeckel's Protista included diverse organisms such as bacteria, protozoa, algae, and fungi.