As well as being one of the US's most celebrated songwriters, Harburg was a lifelong socialist and a victim of the Hollywood blacklist in the 1950s. He remained on the left until his death from a heart attack in 1981.

Yip was born in New York in April 1896, the son of Russian-Jewish immigrants. He was from a socialist family and he became, as he put it, "a rebel by birth". This commitment was to inform his art, leading to the staging on Broadway, of all places, of comic musicals with socialist politics informed by Marxist theory. Most accounts describe Harburg's nickname, Yip, as being short for the Yiddish for squirrel. A much more likely explanation is that it derives from his membership of and identification with the Young People's Socialist League (YPSL).

He first came to prominence as a lyricist in 1932 when he wrote "Brother, Can You Spare a Dime?" This, his first great lyric, was a response to the queues for New York's soup kitchens that went on "for blocks and blocks". It is a cry of anger at the capitalist system in a time of depression and mass unemployment:

"Once I built a railroad/Made it run/Made it race against time/Once I built a railroad/Now it's done/Brother can you spare a dime."

The Wizard of Oz is a film about politics, celebrating liberation. It is a reworking for the 1930s of L Frank Baum's novel, The Wonderful Wizard of Oz, published in 1900. In Baum's children's book, the Tin Man represents the working class, the Scarecrow the small farmer, the Cowardly Lion the populist leader, William Jennings Bryan, the Wicked Witch is big business and the Wizard himself is the US government. In the novel, Dorothy has silver shoes, the populist panacea, but in the film, her shoes are red. One of the film's anthems, "Ding Dong, the Witch Is Dead", was to be sung on picket lines.

Harburg did not just write the songs, but was also responsible for the film's production and he received an Oscar for "Over the Rainbow".

In the late 1930s and early 1940s, Harburg was very much part of the Popular Front movement in the US. He supported militant trade unionism, opposed fascism and was a committed anti-racist.

During the Second World War the US military not only segregated black and white servicemen, but also segregated their blood in its medical services. Harburg wrote a tremendous comic lyric satirising this:

"I went down to that St James Infirmary/And I saw some plasma there and I/Ups and asks the doctor man/Was the donor dark or fair?/The doctor laughed a great big laugh/And puffed it right in my face!/He said, 'A molecule is a molecule/And the darn thing has no race'./.../Why them Aryans who think they're noble/They don't even know the corpuscle is global/Tryin' to disunite us with their racial supremacy/Flyin' in the face of old man chemistry/Takin' all the facts and tryin' to twist 'em/But you can't overthrow the circulatory system."

In 1947, Harburg produced what his biographers describe as his "masterpiece", the musical Finian's Rainbow. It is "a work of socialist analysis in the form of the American musical...the only American musical written in the shadow of Marx on the fetishism of commodities." In a very contemporary moment, Harburg has the pot of gold in the story turn into a chamber pot.

In 1950, Harburg fell victim to the Hollywood blacklist. Although he had never been a Communist, he had supported many of the same causes and up until his death he remained close to the US Marxist journal, Monthly Review.

When he challenged Roy Brewer - the trade union leader who operated the blacklist - to specify his crimes, Harburg was told that one of the marks against him was his 1940 musical, Cabin In The Sky, filmed in 1943. The male protagonist in the all-black production, Little Joe, is a dead soul returned to earth to earn redemption. One of the love songs is "Happiness Is a Thing Called Joe" which in the McCarthyite US had apparently become a love song to Joe Stalin.

Brewer offered Harburg absolution if he recant in writing, an offer he refused with the typical remark that he didn't write for third rate publications.

Harburg's artistic response to the blacklist was the musical Flahooley set in a toy manufacturing company. A biography describes it as a "send-up of corporate culture and the zeitgeist of witchhunts and loyalty oaths...and underpinning the entire piece, its raison d'etre, is a comic contemplation of capitalism's systemic tendency towards overproduction and underconsumption. For better or worse, Flahooley is still our nearest approximation to a musical comedy version of Das Kapital."

Its opening number is a comic indictment of Cold War conformity, "You Too Can Be A Puppet". Forget the Brotherhood of Man and join capitalism's "Brotherwood of Man" instead. Yip Harburg was no one's puppet.