Pentti Siiteri was a brilliant, inquisitive, and outstanding scientist, who delved deeply to get to the core of very significant, important, and novel hormonal findings, no matter how complex the issues. He did not stop digging regardless of how complex the issue, and his investigations were almost always well thought through, and almost always correct. “Finn,” which was what almost everybody called him, had a love and enjoyment of life in general, and science particularly. He had five delightful children, four sons and one daughter, all of whom were extremely fond of their Dad. His delightful wife, Helen, is a successful and perceptive writer of children's books, and a thoughtful, intelligent, charming woman and mother. Among Finn's numerous discoveries were demonstrations of key facets of the human placenta, the early studies of progesterone and estrogens, both physiologically and pathologically, and various forms of cancer. He completed his doctorate at Dartmouth and a postdoctoral fellowship at Columbia University. He studied with the brilliant, perceptive, world-renowned biochemist, Seymour Lieberman, who trained many outstanding biochemists. When Finn was at Columbia University, he also worked closely with Paul MacDonald, a brilliant physician-scientist. Soon after Paul moved back to the University of Texas Southwestern in Dallas from Columbia, Finn joined him in Dallas. They produced a series of very important studies concerning the placenta and free and conjugated steroids, for which Finn was well known and received many honors, including a major formal presentation in Finland. Shortly after I joined the faculty at the University of California, San Francisco, and established the Center for Reproductive Medicine and Biology to enhance basic science in Obstetrics and Gynecology. I was invited to speak at the University of Texas Southwestern, where Finn had been successful and productive for many years. I was looking for a senior biochemist who could help nurture and train more junior physicians and scientists. Finn accepted my offer and soon joined me on the faculty of UCSF in the Center for Reproductive Medicine and Biology, where he had a fruitful scientific career. With Finn as a senior faculty member, we recruited a panoply of talented faculty members, fellows, and graduate students. Aside from his scientific talents, one of Finn's many other abilities included playing a variety of string instruments, including a mandolin, guitar, and ukulele. He often serenaded us with his ukulele and other instruments. Finn was a warm, caring, unique, and wonderful individual. He was one of a kind, and will be missed by family, friends, and colleagues.