Prof. Han-Ill Yoo received his Ph.D in Ceramics from the Department of Materials Science and Engineering, Massachusetts Institute of Technology (MIT), U. S.A. in 1984. He had since been affiliated with the faculty of the Department of Materials Science and Engineering, Seoul National University until his retirement in 2017 and then with the Daegu Gyeongbuk Institute of Science and Technology (DGIST) as an Invited Chair Professor for the next four years. He has taught Thermodynamics and Kinetics while pursuing lifelong research in defect chemistry and the mass and charge transport properties of ceramics. In the course of his work, he discovered an unusual non-superconducting ceramic with vanishing thermopower, established the experimental methods to determine, once and for all, all the mass and charge transport properties of a material in terms of the coupling coefficient matrix of the Onsagerian causality, and experimentally demonstrated the Onsager Reciprocity between ionic and electronic flows in mixed ionic electronic conductors. He is still delving into the thermomigration behavior of ceramics. He was awarded the Alexander von Humboldt Research Award in 2004 and elected a Fellow of the College of Engineering, the University of Tokyo in 2009. From 2017 to 2019, he served as President of the International Society for Solid State Ionics (ISSI). Outside the laboratory, he was an avid high-altitude trekker, having climbed breathless peaks such as Mt. Kinabalu (4095 m), Annapurna Base Camp (4130 m), Mt. Kilimanjaro (5895 m), Lake Gosainkunda (4380 m), Mt. Kala Patthar (5643 m), and Mt. Rinjani (3726 m), among others.