in the Bavaria, Germany, WWI Personnel Rosters, 1914-1918
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Here we go:
in the Baden, Germany, Lutheran Baptisms, Marriages, and Burials, 1502-1985
Index-only record
https://de.wikipedia.org/wiki/Wilhelm_Br%C3%BCckner
Wilhelm Friedrich Karl Brückner (* 11. Dezember 1884 in Baden-Baden; † 20. August 1954 in Herbsdorf)
The Standesamt Baden-Baden should be able to tell you how to get his birth record: standesamt@baden-baden.de