Sometimes in showbusiness, an opportunity presents itself which is too good to turn down - a project whose potential is so obvious that everyone instinctively knows that it will succeed spectacularly.
When actor, director and satirical comic Harry Shearer was offered the chance to voice some of the characters in a new series called The Simpsons back in 1989, he had his answer ready. "Matt Groening [the creator of the series] was a fan of my radio show. I did characters and a lot of satirical stuff. He had his partner, Jim Brooks, called me and ask me whether I wanted to take part. I told him I didn't want to be in a cartoon show. After two or three calls, he managed to twist my arm, and eventually I said: ‘Oh, OK.'"
It was one of the better decisions in Shearer's life. He became the voice of the evil Mr Burns, plus a range of other iconic characters, including Waylon Smithers, Ned Flanders, Reverend Timothy Lovejoy, Kent Brockman and Scratchy the Mouse. He has also voiced a range of guest stars. "I've done everyone from Hitler to Bill Clinton and the Devil," he laughs.
Despite the fact that Shearer is the only one of the main cast who has not received an Emmy (he has been called the Peter O'Toole of The Simpsons, referring to the veteran film star who never won an Oscar), there are compensations - the money, for example. He is said to earn well in excess of £25,000 per episode.
However, this is merely Shearer's day job. By the time he stepped up to the microphone for the first episode, he was already a cult in his own right, as the co-writer and co-star of the 1984 spoof documentary This Is Spinal Tap, which hilariously followed the eponymous fading British rock band on an ill-fated US tour.
Spinal Tap, more than The Simpsons (which is after all Groening's brainchild), sums up Shearer's humour. "It was the first of that kind of spoof. The animating impulse was to do rock 'n' roll right. The four of us [Rob Reiner, Michael McKean, Christopher Guest and Shearer] had been around rock 'n' roll and we were just amazed by how relentlessly the movies got it wrong. Because we were funny people it was going to be a funny film, but we wanted to get it right."
Even after 25 years, Shearer remains happy to chat about Spinal Tap. "I'm very proud that the movie has this life that went way beyond what anyone could have ever expected. If you affect that pose of ‘I'm so bored of the fact this movie is still being quoted by people', you should get out of the business."
He has an interesting perspective on why the movie - which proved once and for all that Americans can do English accents if they try hard enough - was successful. Shearer, who played bass player Derek Smalls, says: "We had so little money to make it that there are very few gadgets or TVs or phones. Nothing ages a movie like obsolete gadgets."
And of course the world of rock and celebrity is also still instantly recognisable from the movie. "Rock 'n' roll doesn't change. All the idiocies and pretension continue."
If Spinal Tap highlighted the gently satirical side of Shearer's nature, his new project, Song of the Bushmen, is more savage. Shearer has been composing and performing satirical numbers about President George Bush and his cronies on his US radio programme, Le Show, for a number of years. It occurred to him that he already had almost enough tracks for an album.
"I had already gathered quite a few songs about these people who work for Bush, so I thought if I write four or five more there will be a musical impeachment, since they clearly won't get any other kind.
"When the popularity rating of this guy is lower than Hitler, it seems like the right time. Satire at its best is fuelled by anger and if you can't get angry at the stuff these people have done you need a hormone transplant. The first track sums it up. The original idea for the proposed bail-out for this economic disaster was for the Treasury Minister to spend $700 billion any way he saw fit. Neither Congress nor any judge would have been able to engage in a review. In other words, they were telling us: ‘We know best, we'll do what we want and nobody else will even know what we're doing. It will be secret and our justifications will be secret.'"
He adds: "There's a lot of concentration by a lot of people on the [US presidential] election. But I'm still keeping my eye on the people who have the power, rather than those who aspire to it. These guys still have four months and they can still do a lot of damage. Bush said famously: ‘I'm going to be sprinting to the finish line.' That scares me."
Shearer delivers the line in an uncanny impersonation of the President. His versatile talents as an impressionist have been a significant factor in his success and, through The Simpsons, he has made enough money to be able to present his weekly radio show without asking for any payment.
So which is his favourite character?
Shearer adopts the persona of Mr Burns, the sinister owner of the nuclear-processing plant where Homer Simpson is employed: "I like Mr Burns because he is pure evil. A lot of evil people make the mistake of diluting it. Never adulterate your evil."
The familiar voice sounds strange coming from a man who is not yellow in the slightest. Actually, Shearer, speaking over a mineral water in a Central London club, looks much younger than his 65 years. His parents were Jewish refugees from the Nazis - his mother from Poland, his father from Austria. They met in Havana, Cuba, while waiting for entry permits into the USA in the late 1930s. They settled in the Pacific North-West before moving to Los Angeles ("thank God") when Shearer's mother was pregnant with him.
The experience of growing up the child of immigrants gave him what he describes as an "outsider sensibility". "I had to teach myself about America and that made me more curious and more exploratory. My dad was a soccer player but knew nothing about baseball. It made me avid about absorbing media."
Did their experiences make them, and subsequently him, political animals? "We always talked about stuff at the dinner table. I don't know whether that had to do with their origins or the way they were,"
He does not see any explicit Jewishness in his work despite the fact that, since his first foray as a child actor on The Jack Benny Programme in the 1950s, he has worked with a disproportionate number of Jews, (including Rob Reiner and Christopher Guest in Spinal Tap).
"I was always amazed that New York Jews were so fixated on their Jewishness," he says. "It seems to me in my work almost irrelevant. I never deal with matters of religion. I don't think it's a good idea to make fun of the stuff that people appear to need in their lives. The self-consciousness of Woody Allen and Philip Roth is in a way the difference between New York and LA. New York imprints you with a tribal identity in a way that LA doesn't - it's much more of an individualistic place. People go there to shed their identities."
Looking back on a career which, given Shearer's obvious energy and enthusiasm for life, is clearly by no means over, he is torn over what has given him the most satisfaction. Spinal Tap spawned a whole genre of spoofs, including most notably The Office, which Ricky Gervais has acknowledged was inspired by the 1984 cult hit. He also loves directing, which is, he says, "like surfing on a wave of problem-solving".
The one project which was less than fun was his 2006 novel Not Enough Indians - a darkly satirical exploration of the Native American community. Without the pleasures of collaboration, spontaneity and improvisation which characterise his other projects, it was a struggle. "The only fun thing about it was having written it. It was lonely, I had no deal for it and it took six years to do. It was a profoundly disturbing act of self-discipline."
Songs of the Bushman is available on iTunes
Born: December 23, 1943 in Los Angeles
Background: His father was Mack, an Austrian-born opera singer who ran a petrol station in the US. His mother was Dora, an Polish-born bookkeeper
Early life: First appeared on radio as a child in The Jack Benny Programme, where he worked for eight years. He also appeared in an Abbott and Costello movie and in the Alfred Hitchcock Presents television show. He studied at UCLA and Harvard before moving into television and film
Career: Best known for the 1984 spoof rockumentary This is Spinal Tap, and The Simpsons, on which he has worked since it started in 1989. He has presented a long-running radio programme, Le Show, on Santa Monica channel KCRW; was a long-time performer on Saturday Night Live; and has appeared in films including A Mighty Wind and For Your Consideration
Family: Married Penelope Michaels in 1974 but divorced three years later. Since 1993 he has been married to Welsh-born singer-songwriter Judith Owen
On his Jewish identity: "In Spinal Tap, Christopher Guest, Rob Reiner and I were all Jewish but we never spoke about it. In fact, we hardly ever had non-comedic conversations. I don't feel that my Jewish identity has much of a presence in my work, although an outside observer may disagree"