Oscar Fetrás (16 February 1854 – 10 January 1931) was a German composer of popular dance music, military marches, piano pieces, and arrangements.

He had over 300 compositions to his name and his best-known is his waltz "Mondnacht auf der Alster" (Moonlight on the Alster) Op. 60 which is still very popular today.

He was born as Otto Kaufmann Faster in Hamburg. His father Matthias Faster was an editor of a stock-exchange magazine. The family originally came from Bützfleth, a locality of today's Stade near Hamburg.

Early in his career he worked for Ferdinand Laeisz  founder of the Flying P-Liner (The Flying P-Liners were sailing ships). Gradually he became widely regarded as being on the same level as the Viennese waltz kings. Aged 26, his compositions attracted the attention of a Hamburg publisher, who advised him to change his name. He changed his name to Fetrás, an anagram of his surname Faster.

It might have been Franz von Blon, at that time the conductor of the Stadttheater Orchestra, who introduced "Moonlight on the Alster" at the inaugural concert for the 1888 ball season. It was a sensation and earned Fetrás the title of "The Hamburg Waltz King". 

He remained well-known and respected and though definitely a second rank composer in the Viennese style, he produced some 300 works. Fetrás died January 1931 in Hamburg and was buried in the Ohlsdorf Cemetery.

In 1943, during the bombing of Hamburg during the Second World War the original score of "Moonlight on the Alster" was destroyed. Much of his work has disappeared from the mainstream repertoire since then. This was primarily due to the many outlets of music publishers and music parts libraries which issued his material being destroyed during the bombing which left no publishers to issue his material to this day.

In Hamburg-Rahlstedt the street Fetrasweg is named after him.

Today, we feature his best known waltz – "Moonlight on the Alster".