Let us now praise obscure men. Those who perform thankless tasks, those who pick up where others have left off, the good enough but not great, we salute you. Roll call, please: Franco Alfano, Friedrich Cerha, Tibor Serly, Anthony Payne, Zoltán Göncz.

Household names if your house happens to be a music library, otherwise unknown to all but the most dedicated program-notes readers.

Yet they are worthy of celebration. They are, respectively, the composers who completed Puccini’s Turandot, Berg’s Lulu, Bartok’s viola concerto, Elgar’s Symphony No. 3 and Bach’s Art of the Fugue.

Riccardo Muti leads the Chicago Symphony Orchestra in Mozart’s Requiem, Feb. 19-21 and 24.

The list of those who have picked up a dropped pen is fairly extensive. Very few composers have planned their lives well enough to pass away just as they complete a work’s final measure. They leave mid-phrase, or are realize they will have time only to leave sketches.

Some of these completed works go on to a long performance life, some don’t. There is a Beethoven 10th symphony floating around, as well as a Tchaikovsky 7th symphony. As to why we still listen to Turandot and why you are, at this very moment, probably thinking Beethoven’s 10th?, there are a lot of factors: how much of a given work is in the original hand, what is the quality of that original work, how gifted a musical mimic the secondary composer is, and how well the completed work holds together.

Despite the risks, expectations, and difficulties that come with stepping into a master’s shoes, these often unsung heroes have soldiered on. If there is one of this intrepid band of brothers who has achieved even slight name recognition, it would be Franz Xaver Süssmayr (1766-1803).

A list of Süssmayr’s completed works includes masses, cantatas, offertories, a magnificat, hymns, a clarinet concerto and several operas. Elegant works, all. They are balanced, melodic  and completely overshadowed by his singular contribution to the standard repertoire: his completion of Mozart’s Requiem.

For the post-war generation, the dominant story that accompanies the Requiem is the one told by Peter Shaffer in the play and film “Amadeus.” Revenge! Jealousy! Murder!

And hogwash.

Meanwhile, a less dramatic but more interesting story attends Süssmayr.

The short version: Mozart had been commissioned to write the Requiem but passed away before completing it. Some of the commission money was due upon completion; in coarse terms, this left money on the table, money that Mozart’s widow Constanze needed. Her first candidate, Joseph von Eybler, contributed some work but eventually gave up and handed the manuscript back to Constanze, who then turned it over to Süssmayr, a friend of Mozart’s who was familiar with the composer’s intentions for the work.

What Mozart left was a fully orchestrated first movement, the vocal parts, figured bass for everything but the Lachrymosa, and suggestions for orchestration in other movements. Certainly more than a fragment, there was much left to be done. Debate over Süssmayr’s contributions continues. Consensus is that four composers put their hand to the plow at some point — Süssmayr, Eybler, Frystadtler and Stabler — but that Süssmayr finished the Lacrymosa and added several sections himself (Sanctus, Benedictus, Agnus Dei). We know he made substantial additions because his work had basic errors that later had to be touched up.

As to whether his contributions are “Mozartean” enough, you’ll get a wide variety of partisans on either side. Several composers have attempted to create “cleaner” versions (hat tip to Sigismund Neukomm, Franz Beyer, Richard Maunder, and Robert Levin). Meanwhile, Beethoven reportedly once said of the work, “If Mozart did not write the music, then the man who wrote it was a Mozart.”

Regardless of the controversies, Süssmayr did yeoman’s duty, enough to keep the work alive and beloved through the centuries. And enough to benefit Constanze well into her old age.

Based in California, Peter Lefevre writes about classical music for the Orange County Register and Opera News.

TOP: Detail from a cover photo of a recording of Mozart’s Requiem.