If you ever imagined that the conductor Michael Tilson Thomas might be Welsh, think again. "Thomas" was originally "Thomashefsky": the name signals an extraordinary heritage that underpins this much-loved maestro's instinct for performance and showbusiness.
He is currently in the UK to conduct the London Symphony Orchestra in a series of concerts focusing on the music of Claude Debussy, the 150th anniversary of whose birth falls this year. And though the Barbican concert hall may seem a long way from New York's Lower East Side and its Yiddish-speaking immigrants of the 1880s, perhaps Tilson Thomas brings something of their spirit with him.
His grandparents, Bessie and Boris Thomashefsky, were prominent stars in the development of American Yiddish theatre in Manhattan. They went on to own theatres in the area, to publish a magazine, to encourage generations of young actors, to raise funds for many social causes and to be at the cutting edge of thespian life in general. After Boris died in 1939, it was reported that a crowd 30,000 strong lined the street on the day of his funeral.
"When I was growing up I was surrounded by people who had a connection with the Yiddish theatre, which had an attitude of great adventure and of social activism," says Tilson Thomas, who is 67. "Much of its repertoire concerned issues of the time: women's rights, labour rights and concerns regarding assimilation, language and more. These issues were put onto the stage so that people could observe them, comment upon them and express different social and political opinions."
They were remarkably free to break new ground: "At this time, about 100 years ago, a lot of plays were prevented from being performed in the US, such as Ibsen's Ghosts. The US premieres of many important theatre works took place in Yiddish, because there was no censorship in the Yiddish theatre."
But the majority of the Thomashefkys' productions were self-created. "They could move from improvisation to producing a complete show in a very short period of time. Often these plays reflected current events, so if there were a flood or a provocative election, within a week or two there'd be a play on stage about it." Every show involved music, songs and an orchestra. "This set the pattern for later developments on Broadway - musicals that were about social issues, like Showboat and Porgy and Bess."
Tilson Thomas has devoted a good deal of time these past few years to a large-scale theatrical project, The Thomashefskys: Music and Memories of a Life in the Yiddish Theatre, that pays tribute to his grandparents and helps to preserve some of their work, especially its music. Having unearthed many of the songs from libraries and archives, and remembering the sound of them clearly himself, he hopes that these works can consequently remain available to successive generations.
His grandfather died before he was born, but his grandmother remained a vital presence in his life until he was 17. "I always knew her as an old lady with amazing stories and an extraordinary personality," he says. "She could be feeling poorly, but the moment there was any audience for whom she could do a song or a recitation, instantly she overcame everything and she had an enormous power of projection.
"Everyone in the family was very musical - none of them had any musical training but they improvised on the violin and piano and came up with songs on the spur of the moment for any occasion. It was a very rich tradition, yet there was a certain playfulness about it."
His own approach as a performer has been strongly influenced by that environment. "I see the role of a conductor as being like that of a theatre director. I'm working with great performers and my objective is to create a situation in which they give a great performance. I'm not saying to them: 'Play the first two notes shorter, the next two a bit longer and the next two a bit louder', because you would never say that to an actor. You want the actor to have the opportunity to become the part. And it's the same with music - you want the performers to call upon their love and understanding of music and to feel free to share that with the audience."
Tilson Thomas maintains "a few little observances" where his Jewish heritage is concerned, but it is the "Yiddishkeit" tradition that runs deepest in his spirit.
"My family started off as cantors or badchens; for many generations they were one or the other, sometimes both. But gradually they were more and more attracted to the theatre and to abstract music. So, more than most people my age, I have a strong stance on what the flavour of this world was like. There's a certain perspective involved: a degree of critical examination and the questioning of many, many things."
The music of Debussy has long been a passion for Tilson Thomas - one of his proudest achievements, he says, was the recording he made in the early 1990s with the LSO of Le Martyre de Saint Sébastien, the composer's 1911 five-act mystery play. The current LSO concert series brings together well-known works and under-recognised ones, alongside contrasting pieces by Berlioz, Kurt Weill and others.
"Debussy's music seems to open a new world for us," says Tilson Thomas. "He was able to use notes in a very concentrated way to evoke many things in the sensual side of our experience. It's easy to hear the influences in his music - Wagner, Mussorgsky, Gamelan music, Middle Eastern music, folksongs, material of all different sorts - yet there is something utterly original, mysterious, somehow both ecstatic and mournful."
Intriguingly, Debussy's second wife, Emma Bardac, was Jewish; how that impacted on Debussy and his music is something that might merit exploration in the future.
Tilson Thomas divides his time between two posts on opposite sides of the United States - on the west coast, he is music director of the San Francisco Symphony Orchestra, and on the east coast, in Miami, he remains artistic director of the New World Symphony, a vital training ground that attracts some of America's finest young orchestral players.
But now his immediate joy is to be back with the LSO, the orchestra with which he conducted his first concert in Europe some 40 years ago. Ever since, he has rarely been away from them for long. "I'm delighted to be back in London, with my great colleagues in the LSO," he declares. "I always tend to hang on to relationships with groups I've liked. I feel we have a shared tradition, like a family."