One conspicuous absentee from the 20th anniversary celebrations of the fall of the Berlin Wall was former British prime minister Mrs Thatcher. We saw 85-year-old George Bush senior leaning on a cane, former Soviet leader Mikhail Gorbachev looking decidedly podgy and the always very ample-girthed Helmut Kohl now wheelchair-bound. But Thatcher has fared worst, apparently lost in senile dementia. Perhaps that’s why she wasn’t there. Or was it that she had never shared the exuberance over a united Germany in the first place?

Flashback 20 years. Thatcher was entering the last year of her rule and was facing a challenge from a "stalking horse" candidate. A year later came the more deadly challenge from Michael Heseltine. Thatcher was the lightning rod for everyone of mildly left persuasion. Was it her policies or her personality that so inflamed people and evoked such strong reactions either way?

Sometimes I wonder if very similar policies had been pursued by another female politician people felt was "caring" and "compassionate" - Shirley Williams perhaps - would she have been so controversial? Personalities, you see, are important. Perhaps they shouldn’t be, but they are. Thatcher radiated an icy authority - the late Alan Clark said she was one of the few politicians he had ever seen who displayed no nerves at the dispatch box in the house of commons. George HW Bush, on the other hand, always seemed diffident and slightly mincing. Even when he launched the first Gulf War in 1990 he came across as the eternal victim in the school locker room who had finally decided to fight back.

Reagan, for all his critics, had a kind of natural authority about him. Thatcher’s opponent 20 years ago, Labour leader Neil Kinnock, simply didn’t look like a prime minister; regardless of the black sober suits and glasses he acquired, he had the air of a Welsh "boyo" who we’d be happy talking to at a rugby match. But prime minister? Forget it!

When a powerful personality comes along, we tend to project onto them all kinds of qualities and we become merely vassals. We also lose our objectivity. Charisma breeds hysteria. This kind of presence comes not from physical stature exclusively, but from something mystical and intangible from within. By all accounts Hitler was a physical wreck for at least the last year of his life, yet, despite the suicidal nature of his domestic and foreign policy, he was the one person whose orders were always obeyed unconditionally. (You may wince but David Bowie described Hitler as the 20th century’s first superstar).

This gravitas or authority - whether in people we deem great (or evil such as Hitler) - must be from birth. There is no other explanation. Significantly, most Hollywood "legends" have been blue-eyed, film stars like Newman, Dean, Brando, Monroe, Eastwood, Wayne and Sinatra, as well as the world leaders we have deemed most charismatic: Kennedy, Reagan, Clinton, Thatcher and Blair.

Barack Obama is a notable exception. Does this mean people in the West tend to associate blue eyes with purity of character? This kind of analysis would contravene the rules of political correctness but it’s crucial, nevertheless, for understanding human malleability. Answers on a postcard, please.