Ferdinand I (26 February 1861 – 10 September 1948), born Ferdinand Maximilian Karl Leopold Maria of Saxe-Coburg and Gotha, was the ruler of Bulgaria from 1887 to 1918, first as knyaz (prince regnant, 1887–1908) and later as tsar (king, 1908–1918). He was also an author, botanist, entomologist and philatelist.