Sir Marcus Gunn was a prominent British ophthalmologist born in 1850. He is best known for his work in the field of eye surgery and for describing the Marcus Gunn pupil, a condition where one pupil reacts differently to light than the other. His research significantly advanced the understanding of neurological conditions affecting vision. Gunn was also a pioneer in the development of surgical techniques for cataract removal and other eye disorders. He served as a professor at University College London and contributed to various medical journals, influencing future generations of ophthalmologists and enhancing the field of eye care.