We lost our beloved PhD mentor, Susumu Tonegawa, leaving an emptiness. Whenever I think about courage, I think about Susumu. He switched fields twice and relearned everything. Whenever I think about greatness, I think about Susumu. He was on a mission to discover how Nature works for the benefit of humanity. Whenever I think about perseverence, I think about Susumu. There is a funny anecdote we knew that when he climbed the great wall of China at a scientific conference, he wanted to race everyone to the top and was perplexed when all the (younger) faculty members were much slower than he was. He was a lion of a man. A dear friend from the lab once told me that seeing science through his eyes has been one of the highlights of his life. It is mine as well. I think this poem that by Ki no Tsurayuki expresses well what I feel , which I think others who have lost mentors can also feel 色も香も昔の濃さに匂へども 植ゑけむ人の影ぞ恋しき Blossoms deep in color and fragrance as in the old days, yet I long for the one who first planted them. Photos from happier days: