William Addams Reitwiesner (March 8, 1954 – November 12, 2010) was an American genealogist who traced the ancestry of United States political figures, European royalty and celebrities.

After graduating from Montgomery Blair High School in 1972, Reitwiesner joined the Library of Congress's Congressional Research Service (CRS) as a cart pusher.

He spent the rest of his working life in menial jobs at the Library of Congress so that he could devote his time pursuing his interest in genealogy.

[1] Although much of his work was self-published on the internet, he acquired a reputation for meticulousness and accuracy[1] and many genealogists cited him in their publications.

[1] Genealogies that Reitwiesner published include:[2] Although Reitwiesner's original website is now in abeyance (www.wargs.com), much of his research that was published online can still be accessed using archive websites.