Ferdinand I (Bulgarian: ????????? I; 26 February 1861 – 10 September 1948), born Ferdinand Maximilian Karl Leopold Maria of Saxe-Coburg and Gotha, was the second monarch of the Third Bulgarian State, firstly as ruling prince (knyaz) from 1887 to 1908, and later as king (tsar) from 1908 until his abdication in 1918.
He was also an author, botanist, entomologist and philatelist.