Background: Jose Rizal was born in 1861 to Francisco Mercado and Teodora Alonso in the town of Calamba in Laguna province. He had nine sisters and one brother. His parents were leaseholders of a hacienda and an accompanying rice farm by the Dominicans. Both their families had adopted the additional surnames of Rizal and Realonda in 1849, after Governor General Narciso Claveria
Context: Rizal first studied under Justiniano Aquino Cruz in Binan, Laguna, before he was sent to Manila. As to his father's request, he took the entrance examination in Colegio de San Juan de Letran but he then enrolled at the Ateneo Municipal de Manila and graduated as one of the nine students in his class declared sobresaliente or outstanding. He continued his education at the Ateneo Municipal de Manila to obtain a land surveyor and assessor's degree, and at the same time at the University of Santo Tomas where he did take up a preparatory course in law. Upon learning that his mother was going blind, he decided to switch to medicine at the medical school of Santo Tomas specializing later in ophthalmology.  Without his parents' knowledge and consent, but secretly supported by his brother Paciano, he traveled alone to Madrid, Spain in May 1882 and studied medicine at the Universidad Central de Madrid where he earned the degree, Licentiate in Medicine. He also attended medical lectures at the University of Paris and the University of Heidelberg. In Berlin, he was inducted as a member of the Berlin Ethnological Society and the Berlin Anthropological Society under the patronage of the famous pathologist Rudolf Virchow. Following custom, he delivered an address in German in April 1887 before the Anthropological Society on the orthography and structure of the Tagalog language. He left Heidelberg a poem, "A las flores del Heidelberg", which was both an evocation and a prayer for the welfare of his native land and the unification of common values between East and West.  At Heidelberg, the 25-year-old Rizal, completed in 1887 his eye specialization under the renowned professor, Otto Becker. There he used the newly invented ophthalmoscope (invented by Hermann von Helmholtz) to later operate on his own mother's eye. From Heidelberg, Rizal wrote his parents: "I spend half of the day in the study of German and the other half, in the diseases of the eye. Twice a week, I go to the bierbrauerie, or beerhall, to speak German with my student friends." He lived in a Karlstrasse boarding house then moved to Ludwigsplatz. There, he met Reverend Karl Ullmer and stayed with them in Wilhelmsfeld, where he wrote the last few chapters of Noli Me Tangere.  Rizal was a polymath, skilled in both science and the arts. He painted, sketched, and made sculptures and woodcarving. He was a prolific poet, essayist, and novelist whose most famous works were his two novels, Noli Me Tangere and its sequel, El filibusterismo. These social commentaries during the Spanish colonization of the country formed the nucleus of literature that inspired peaceful reformists and armed revolutionaries alike. Rizal was also a polyglot, conversant in twenty-two languages.  Rizal's multifacetedness was described by his German friend, Dr. Adolf Bernhard Meyer, as "stupendous." Documented studies show him to be a polymath with the ability to master various skills and subjects. He was an ophthalmologist, sculptor, painter, educator, farmer, historian, playwright and journalist. Besides poetry and creative writing, he dabbled, with varying degrees of expertise, in architecture, cartography, economics, ethnology, anthropology, sociology, dramatics, martial arts, fencing and pistol shooting. He was also a Freemason, joining Acacia Lodge No. 9 during his time in Spain and becoming a Master Mason in 1884.
Question: Who did he study under?. Whats the answer?
At Heidelberg, the 25-year-old Rizal, completed in 1887 his eye specialization under the renowned professor, Otto Becker.