Ben Ashkenazy bought his first piece of property when he was right out of high school, with a little help from his dad. Three decades later, his collection boasts some of America’s best-known buildings. He keeps a very low profile for someone whose company has a $12 billion portfolio --including Boston’s Faneuil Hall Marketplace, Washington’s Union Station and a piece of the Plaza Hotel in New York -- and just paid about $750 million for the Grosvenor House hotel on London’s Park Lane. Ashkenazy Acquisition Corp. itself had to scale a name-recognition hurdle to make an earlier deal in the British capital. Ashkenazy Acquisition had built an empire of retail, hotel and office assets. And its 48-year-old founder and chairman was amassing a fortune, one that made it possible for him to hire the rapper Drake to perform for his daughter’s bat mitzvah at the Rainbow Room last year. Ashkenazy’s net worth is $4.1 billion, according to the Bloomberg Billionaires Index, vaulting him into the ranks of the world’s 500 richest people. Ashkenazy Acquisition owns dozens of other properties, including San Francisco’s One Union Square, the Barneys store buildings in New York and Beverly Hills, Harborplace in Baltimore and the former church in Manhattan’s Chelsea district that once housed the Limelight nightclub. Born in Israel and raised on Long Island, Ashkenazy started early, under the guidance of his father, Izzy, a retailer and property investor. As Ashkenazy Acquisition grew, it occasionally joined forces with some of the world’s richest people, including New York’s Gindi family, owners of Century 21 Department Stores Inc. Ashkenazy and his partner, Michael Alpert, friends since high school, are hard-charging. Ashkenazy Acquisition said in July it plans to add $2.3 billion of “global iconic assets” during the next two years.