To an outsider, he looks the antithesis of British drizzle. He evokes sunshine and pleasure with his grammatically relaxed, consonant-slurring Hispanic English, his sudden gleeful laughter as he describes an enthralled visit to the V&A, his warm brown skin. He is that rarity: a black ballet dancer, one of only two (with Jerry Douglas) in the Royal Ballet. Where modern dance has both attracted and accepted all human shades, ballet - middle-class and rarefied - has deterred black children, and ballet companies have failed to welcome black dancers.
New ballet is tentatively trying to become colour-blind; and in an art form where talent - especially male talent - is scarce, directors can discover the advantage of enlarging their pool of choices. Acosta, who joined this season, is a real star for a company that has become more a collection of black holes than a galaxy of heavenly bodies.
We wait to see how well he will suit the gentle filigree of Ashton's Fille, although he has briefly dipped into Ashton before, with a secondary part in English National Ballet's Romeo and Juliet. But, during the Royal Ballet's October-November programmes at Sadler's Wells, he astonished audiences in Raymonda Act III, partnering the exquisite Miyako Yoshjida.
They saw a dancer who slashes across space faster than anyone else, who lacerates the air with shapes so clear and sharp they seem to throw off sparks. He is no mere step-trickster, either: his Russian-derived Cuban training has given him elegance and subtlety.
In a country other than Cuba, where the population is racially mixed and vocational dance training is free, all the odds would have been against him. Born 25 years ago in a poor district of Havana, he was the youngest of 11 children, a kid with excess energy who played football, break-danced on the street, and stole fruit. But his father, a truck driver, had a neighbour whose two sons were at ballet school. He realised that such an establishment would not only curb his nine-year-old son's hyperactivity, but would also educate and feed him.
"So he enrolled me," Acosta says. "And, of course, I started to have problems because I thought ballet was sissy. I skipped the classes and exams, and when I was 13 they fired me." His persevering father found another ballet school, where he could become a boarder this time and the teachers could keep a closer watch on him. And soon afterwards, Acosta had his first sight of the superlative National Ballet of Cuba. Proud of his own physicality, he was awe-struck by the dancers' honed athleticism and determined to be like them.
At the National Ballet School of Cuba he won four competitions, including the prestigious Lausanne and Paris contests. He joined English National Ballet for the 1991-2 season, but his stint was cut short by a bone spur in his ankle. After an operation, he became a member of the Cuban Ballet, guested with the Houston Ballet and eventually transferred there permanently.
Houston, one of the US's leading companies, gave him widely varied roles. American audiences and critics went wild about him; Houston's director, the choreographer Ben Stevenson, encouraged and fine-tuned him.
Dancers may be grateful disciples, but they are also greedy prowlers, scanning the horizon for fresh challenges. Acosta's eyes alighted on the Royal Ballet. In Houston, talking in a buzzy sushi bar, he had been full of excitement about his move, which included his girlfriend Tiekka Schofield, another Houston principal, who has opted for a freelance career. In London, at the Royal Ballet School, sitting in a maths classroom grimly crammed with empty desks, he seems anxious - as well he may be. Since arriving, he has been glad to learn new roles; it is what he came for. But just three - Raymonda, Fille and a supporting part in Forsythe's In the Middle, Somewhat Elevated - a total of 11 performances in three months, is hardly a crushing schedule. "I didn't expect the special treatment I had in Houston," he says. "But I came to London to dance, and I've not had much so far."
He realises things may improve and is impressed by the company's large selection of teachers, each with a different input. But he misses Ben Stevenson's unifying presence. Stevenson is the Houston Ballet, a father guiding and driving his close-knit family, while the Royal Ballet is a looser, more international and grown-up ensemble. "In Houston everybody had to be in class every day and Ben would show you how he wanted things, how to improve. Here you are on your own. If you want to work, it's fine; if you don't, it's up to you.
"It's OK for me; I know how to get on with things. But it could be difficult sometimes, because if you do something wrong, it's much more hard for you to realise than for other people watching. I still have a lot to learn - I don't want to be the same dancer five years from now. I would like to have different tools and to find nourishment through as many roles as possible."
Like all dancers, he is preternaturally aware of the clock ticking. He has - what? - 10 or 12 years left? He has arrived at the Royal Ballet in turbulent times. Perhaps the company's recent flamboyant male defections will bring him more performances. If the Royal Ballet, in this New Labour era, are to be a People's Ballet, they would be crazy not to capitalise on the politically and artistically impeccable presence they now have in their midst.
`La Fille mal gardee' opens at the Royal Festival Hall on 29 Jan.