President-elect Barack Obama will soon be one of the most heavily guarded men in the world, if he is not already.

For the next four years and beyond, Obama will be followed everywhere he goes by the secret service, a crack team of security agents known for their large physiques, stony countenances, dark suits and radio earpieces.

As the first African American to be elected president, Obama is likely to face unprecedented threats on his life. Indeed, police and federal officials have already broken up at least two assassination plots, although it is unclear how serious either was. The secret service began guarding Obama in May 2007, the earliest ever in an election season.

"Changes in the administration certainly necessitate a large operational planning and implementation in terms of our protective mission," said secret service spokesman Ed Donovan, who declined to give any more detail about the security regime.

In an indication of the level of protection Obama can expect, the stage on which he gave his victory speech in Chicago last night was shielded by a canopy of bullet-proof glass.

"Presidents have full-time protection 24-7, everywhere they go," Donovan said. "Everything they do is advanced by secret personnel, throughout the world." Secret service agents will also guard Obama's family, as well as vice-president-elect Joe Biden and his family.

Some presidents have found the 24-hour security cocoon suffocating and the agency's safety demands stifling.

Obama recently remarked that he dreams about driving a car, something he has not done in more than a year.

Upon taking office in 1977, Jimmy Carter was unhappy to see security officials hovering about the White House everywhere he went, opening doors for him as he approached. He told them to keep their distance so he could have some solitude.

The secret service made Bill Clinton stop his regular morning jogs, fearing an assassination attempt, and in his memoirs, Clinton writes of his frustration at having to accommodate the secret service's concerns in other matters such as international travel.

But President Lyndon Johnson is reported to have found co-conspirators among his secret service detail. According to journalist Ronald Kessler's 1995 expose of the executive mansion's inner workings, Inside the White House, the secret service installed a buzzer to warn Johnson when his wife Lady Bird was approaching the Oval Office, lest he be caught in a tryst with one of the comely secretaries he hired.