Short answers, pulled from the story.
Ignaz Xaver Ritter von Seyfried (the 15th of August 1776 - the 27th of August 1841) was an Austrian conductor, composer, and editor who spent nearly three decades as musical director at the Theater an der Wien in Vienna. He conducted the 1805 premiere of Beethoven's Fidelio, preserved eyewitness accounts of Mozart's The Magic Flute premiere, and taught pupils including Eduard Marxsen, who later taught Johannes Brahms.
According to a statement in Seyfried's own handwritten memoirs, he was a pupil of both Wolfgang Amadeus Mozart and Johann Georg Albrechtsberger. Albrechtsberger was one of the most respected counterpoint teachers of the era.
Seyfried conducted the premiere of the original version of Beethoven's Fidelio in 1805. He also provided biographical information about Beethoven in an appendix to Studien im Generalbasse, material described as being of great biographical value and as authentic fact.
Seyfried arranged Beethoven's Three Equals for four trombones, catalogued as WoO 30, for four-part men's chorus. That arrangement was performed at Beethoven's funeral.
Seyfried's pupils included Franz von Suppe, Heinrich Wilhelm Ernst, Antonio Casimir Cartellieri, Joseph Fischhof, and Eduard Marxsen. Marxsen is particularly significant because he went on to teach Johannes Brahms.
The Grove Dictionary stated that Seyfried's versatility won him a unique place in Vienna's musical life, but that almost none of his music is marked by real originality or distinction. A biography published in 1836 required five pages just to list his works.