Dirac's Efforts to synthesize Quantum Mechanics and Special Relativity

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Einstein formulated his theory of special relativity in 1905. Many people say this is an outdated theory. These days, you have to talk about Einstein's general relativity having to do with the universe and happenings in far-away places. On the other hand, is the formula E = mc2 outdated?
Paul A. M. Dirac is the name familiar to all of us. He wrote many papers in a number of different directions. What was his main interest?