Mark S. Zimmer is an attorney in Wisconsin, who has been a classical music and Beethoven devotee ever since putting the LP of Beethoven's Eroica Symphony, with Toscanini conducting the NBC Philharmonic, on the turntable some 50+ years ago and being blown away by the power and the drama that can only be conjured up by music. As Mark likes to say, "It knocked my socks off. And then it knocked off my shoes and messed up my hair."

Mark has since 1999 been the project director of the award-winning The Unheard Beethoven website (https://unheardbeethoven.org), which is devoted to making available hours of free synthesized recordings of unrecorded and unpublished Beethoven compositions. Along the way, he and website musical director A. Willem Holsbergen have done reconstructions of a number of unfinished Beethoven works, including the Macbeth Overture, performed by the National Symphony in 2001 and recorded several times since then, several symphony movements, various dances, and the lost oboe concerto. Their work was also recorded in the Inedita volumes of Unknown Beethoven compositions released in Italy.

In 2014, Zimmer and Holsbergen discovered a previously lost Beethoven song that since 1822 had been known only from a price list Beethoven sent to a prospective publisher. Their successful quest to rediscover the lost song and the poem upon which it was based was recounted in Mark's article published in The Musical Times, Winter 2016 issue.

Zimmer and Holsbergen were also involved in the creation of the Deutsche Grammophon and Naxos Beethoven 2020 box sets, providing scores and background information to these labels. Slowly, the list of unrecorded Beethoven works has dwindled substantially, but there are more Beethoven works still to be recorded, so the job is not yet complete.

Since 2020, Mark has been writing the daily Beethoven 200 Years Ago Today column hosted on The Unheard Beethoven's Facebook page and the website's blog. This column, based upon the surviving conversation books of Beethoven, his letters and contemporary newspapers and magazines, attempts to reconstruct the composer's life on a daily basis, sometimes down to his shopping lists and what he and Nephew Karl had for dinner. Along the way, Beethoven's musical works are documented in detail as they are created, sketched, revised, published and performed, as are the conflicts with his brother, his publishers, his servants, his landlords, and sometimes even his friends. At the same time, we see the generous, loving, and caring impulses behind such immortal works as the Ninth Symphony. The goal of this project is to make the icon relatable and understandable in his time as a real human being, with his flaws as well as the spark of genius.