Dr. Leonard Hofstadter, portrayed by Johnny Galecki, is an experimental physicist with an IQ of 173 who received his Ph.D when he was 24 years old. He shares an apartment with colleague and friend, Sheldon Cooper. He and Penny dated at one point during the series, but they broke up during season 3. They start dating again in season 5 though their relationship has been rocky since Leonard proposed to Penny in bed. Throughout season 6, Penny and Leonard became more comfortable as a couple with Leonard asking Penny to propose to him when she was ready.
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