Gustav Mahler was born in 1860 in Kalischt, Bohemia, and grew up in Iglau, Moravia. He had an affinity for music even at an early age, and at age fifteen entered the Vienna Conservatory. He excelled there, where his fellow students included Hugo Wolff and his teachers included Anton Bruckner. There he completed a String Quintet, considered the finest of his juvenilia, and the cantata Das Klagende Lied, considered his first mature work. Its harmonic language is shockingly original, and was incredibly passed up for the Beethoven Prize in composition for its radicalism (by a jury that included Brahms). He then embarked on a highly succesful conducting career, which would take him to the heights of the profession, including the Vienna Opera and New York Philharmonic. He conducted many premieres, including almost all his works and the New York Premiere of Rachmaninoff's 3rd Piano Concerto with the composer at the piano. However, this is not where his legacy lies nowadays. Rather, it lies with his music.
Gustav Mahler's 1st symphony began its genesis as a symphonic poem named "Titan", based on an obscure romantic poem. It premiered during his stay as conductor of the Budapest Opera, and the work was greeted with confusion at best, specifically the third movement, which turns Frère Jaques into a funeral march and intersperses klezmer wedding music into the funereal atmosphere. Such music had never been heard before, and the work was a critical failure. It is now perhaps his most popular work.
The Symphony #2, "Resurrection", is another contender for the status of Mahler's most popular work. Set in 5 movements, this work picks up where the 1st symphony left off, the first movement being a funeral march for the hero of the 1st symphony, and the work culminates in his resurrection. In the opinion of the author this marks a truly massive step up for Mahler, the symphony in which he truly gives the first demonstration of what he is capable of. It includes a wonderful 4-minute Urlicht, or "Primal Light" which showcases Mahler's talents in the field of lieder, as well as a massive last movement with full orchestra and chorus. Truly a masterpiece of a master.
The Symphony #3 represents a change for Mahler. Unlike the Sturm und Drang qualities of the first two symphonies, the 3rd is a paean to nature. However, even by Mahler's standards, this is a massive work, cast in six movements that span 2 hours. Always somewhat out of favor due to its immense length, it is nevertheless one of the masterpieces of a master, and an enormously complex piece. The conclusion, originally titled "What Love Teaches Me" is perhaps his finest slow movement other than the adagietto.
Unlike the first 3 symphonies, the fourth is rather light at heart, and unlike 2 and 3, cast in the traditional 4 movements. The last of the 3 Wunderhorn Symphonies, this light hearted piece has always been a crowd-pleaser, especially the wonderfully giddy finale.
The fifth symphony represents perhaps Mahler's most popular work, if only for one movement. While most of the work is typically (and gloriously) Mahlerian, The Adagietto is something else. Set essentially for the strings, this piece perhaps conveys sorrow better than anything else Mahler wrote. Played at RFK's funeral as well as in the film Death in Venice, this movement (the fourth of five) makes this probably Mahler's most popular symphony.
The Sixth symphony, the "Tragic", is my personal favorite. The only one of Mahler's symphonies in the traditional four movements with a traditional orchestra (save for the sledgehammer, more on that later). Perhaps the work that conveys the words Allegro con Brio better than any other, this violent work goes through 73 minutes of anguish, coming to a close when the percussionist slams a slegehammer twice into the stage. Recommended for all.
The Seventh is Mahler's most difficult symphony, both for the listener and players/conductor. Sometimes called the "Song of the Night," this work has never been popular with audiences, and is only recommended for experienced Mahlerians. I personally love it, but this is not always agreed with by others. Do not confuse the two Nachtmusik movements from this symphony with Mozart's Eine Kleine Nachtmusik.
Mahler's Eighth, the "Symphony of a Thousand", was his greatest success in his time. It is therefore ironic that it is my least favorite work of his. Set to an orchestra of mammoth proportions (thus the name "Symphony of a Thousand"), this work sets the hymn "Veni Creator Spiritus" and the second part of Goethe's Faust (conclusion) to music. Falmboyant and massive, it is still popular.
Mahler, noting how many composers had died after writing their ninth symphony, attempted to cheat death by writing one unnumbered "Symphony of Songs". Das Lied von der Erde ("The Song of the Earth") is based on German translations of ancient Chinese poetry. Set in six movements and totaling one hour, it concludes with a half-hour movement entitled Der Abschied (The Farewell). Not to be missed.
Mahler then did write his ninth symphony, and it would be his last completed work. Set in four movements and lasting eighty minutes, this work's only rivals in desolation are the uncompleted tenth and the finale of the Tchaikovsky Symphony #6. A wonderful piece, but not for beginners.
Mahler only completed the Adagio to the Tenth Symphony (there is an uncompleted movement with the wonderful title of purgatorio and a completed version by Deryck Cook). As with the ninth, this is heavy material, even more so. Not for beginners, but certainly a masterpiece.
Mahler also wrote a great deal of lieder. If one is comfortable with the lieder format, they are highly recommended. Otherwise, start with Schubert.