Classical Tango Music:
The tango was born in Argentina in the late 1800's from a mix of native, European and African music, rhythms and dances. The tango dance predates the tango music, and was developed dancing to all the music brought by the different immigrants. As tango music evolved into a distinct form, so the dance also progressed. The period between 1937 and 1944 is called the Golden Age of Tango, but more casually music from the mid 20's to early 50's is referred to as Golden Age or Classical Tango. This is when Tango was incredibly popular in Buenos Aires, and all the great orchestras were playing nightly to packed halls. Some of the most famous orchestra leaders are: Francisco Canaro, Carlos Di Sarli, Juan D'Arienzo, Rodolfo Biagi, Alfredo De Angelis, Anibal Troilo, Francisco Lomuto, Edgardo Donato, Miguel Calo, Angel D'Agostino and Osvaldo Pugliese. Similar to swing, which also flourished at this time in North America, the best has been saved, and the music is wonderful, but often marred by poorer quality recordings.
Modern (Nuevo) Tango Music:
After the 1950's, the political situation in Argentina discouraged large gatherings for social dancing, and tango evolved into a show dance. The music became more dramatic, and more influenced by jazz. The greatest maestro of this era was Astor Piazzolla. He experimented with other musical forms such as opera and symphony. Initially, his tangos were very controversial in Argentina. As he gained recognition in Europe and North America, he also gained acceptance in Argentina. Even though he is now considered one of the most influential composers of tango, many dancers still feel that his music is for listening only, rather than dancing. Many popular artists have covered or remixed Piazzolla's music.
In the late 90's, tango once again merged with different musical forms and the next stage of nuevo tango was created. Some are reworks of classical or piazzolla tangos, others are original songs with tango rhythms. Gotan was one of the earliest bands of this style; however, there are many others now: Bajofondo, Carlos Libedinsky, Tanghetto, Otros Aires and Electrocutango.
Alternative Tango Music:
True to it's history of constant evolution of dance and music, and with exposure to other dance forms and music, tango dancers have started to ask, "What other music could we dance tango to?" It turns out many types of music work well with tango: blues (slow swing), klezmer, hard rock ballads (tango was made for Metallica), fado, hip hop, funk etc. Around the world, at tango festivals and regular milongas, DJ's are experimenting with different types of alternative music. Alternative music can also help to make tango more approachable to new dancers.
Tango dance and music is a living and changing art form. What is considered controversial today might be conservative and universally accepted in 10 or 20 years.