The 2021 AMCA Memorial Lecture honors Lewis T. Nielsen, Ph.D., 1920–2014 on the centennial of his birth. Dr. Nielsen was born August 6, 1920, in Salt Lake City, UT. Other than the four years he served in the US Army during World War II, Nielsen lived his entire life in Salt Lake City. He was the eldest of four children, with two sisters and a brother. His father, Knute Lester Nielsen, was injured during World War I, and Nielsen credited his father's disability pension for supporting the family during the Great Depression and allowing “Lew” to pursue his education rather than having to work to support the family.Nielsen's lifelong love for the study of mosquito biology and systematics evolved serendipitously. After failing a junior high school algebra class, he was kept after school writing equations on a blackboard. At about this time a teacher by the name of Archibald took an interest in him and urged him to think seriously about his future and to continue his education. It was at this early age that Nielsen began developing an interest in natural history. While earning a nearly straight-A average in high school, he took botany and zoology, which further fueled his interest in natural history.Following high school graduation at the age of 17, he entered the University of Utah in the fall of 1937, which began a lifelong association with the “U.” While working his way through college, he was assigned a position in the Zoology Department pinning mosquitoes for Don Rees. That led to a summer job at the Salt Lake City Mosquito Abatement and ultimately his life's work with mosquitoes. His three degrees in biology included a B.S. (1941), M.A. (1947) “On the Biology of Aedes dorsalis,” and Ph.D. (1955) “The Taxonomy, Biology and Control of the Rocky Mountain Aedes Mosquito Species.” The intervals between degrees included a tour of duty in the US Army, 1942–1946, and the difficult task of teaching introductory biology classes as an instructor at the university while working on his doctorate. In 1956, Nielsen was promoted to Associate Professor and taught Entomology, Medical Entomology, Insect Morphology, Insect Sociality, Mosquito Systematics, and a general education course he developed called Insects and Man. In 1965, he became the Director of General Biology and was promoted to the rank of Professor in 1966. During his academic career, Nielsen had 29 students that received their Master of Science degrees and 10 students that received their doctorates. He published 82 scientific publications and was the lead author on 41 of those publications. At retirement in 1989, after 43 years teaching and research at the University of Utah, he received the honor of being named Professor Emeritus of Biology.Nielsen played a major role in local mosquito research and control. No one knew more about the biology and taxonomy of Utah mosquitoes. His favorite mosquitoes were the snowmelt mosquitoes of the higher mountainous elevations. He twice served as the President of the Utah Mosquito Abatement Association (UMAA) (1958 and 1990) and was awarded the UMAA Don M. Rees Award in 1988 and the Meritorious Service Award in 2005. For more than 40 years, he organized the association's annual spring training workshop. From the inception of the UMAA in 1948 until his death, he never missed an Annual Meeting of the UMAA.Nielsen had a very close relationship with the American Mosquito Control Association (AMCA). He served as the AMCA President (1977) and received the Medal of Honor Award (1988), was made an Honorary Member (1994), and was awarded the John Belkin Award (2000). He was the Editor for AMCA's Mosquito Systematics publication from 1979 to 1992, Coeditor 1992–1993, and Editor Emeritus 1993–1995. In 1997, Nielsen gave the Memorial Lecture entitled “In Honor of Stanley Carpenter.”Lew's love for the outdoors continued unabated into his nineties including hunting and fishing trips with life-long friends who shared his appreciation for the beauty of nature.