To an outsider, Thursday’s contest to elect the next mayor of London would appear to be a fight between two larger-than-life characters — known best by their first names — for control of the city’s famous red buses. Among a wide field of candidates, only these two men have any realistic chance of taking a starring role at this summer’s Olympic Games in London: Conservative Party incumbent Mayor Boris Johnson, 47, and his 66-year-old nemesis, Labour left-winger and former Mayor Ken Livingstone. Both men have devoted their energies to transport — and attacking each other viciously on the issue, as well as on their complex personal tax arrangements. With his distinctive nasal south London accent, Livingstone rose to fame in the early 1980s as leader of the Greater London Council. Livingstone — populist, socialist, environmentalist — was one of the few who stood up to Margaret Thatcher, the Conservative prime minister at the time, earning him the moniker “Red Ken.”