Thomas Legler, officer in the 1er régiment Suisse.
His recollections (written in German) of 1812:
https://books.google.de/books?id=viwLAAAAIAAJ&pg=PA7
And of 1814 and 1815:
https://books.google.de/books?id=E3EvAAAAYAAJ&pg=PA441
On the morning of 29 November 1812, his commander asked lieutenant Legler to sing a song to him, which he had sung some times before: "Unser Leben gleicht der Reise ..." (our live resembles the voyage of a wanderer in the night). A hundred years later, this song became famous as the "Beresina-Lied", popular legend wanted it to have been sung by all the Swiss soldiers at the Beresina.
The song:
https://www.youtube.com/watch?v=87BW1xwbNLc
Some more info about the song here (in French):