Slapstick enchants children.

And few were better at slapstick than those giants of glee, Hanna Barbera.

When my world was young and we only had a tiny black-and-white telly sandwiched into the corner of the room, my brothers and sisters and I used to watch one of their cartoons. We hung on every word. It was called Hong Kong Phooey.

The hero was a dog, which suited us all very well. During the day, he was Henry, the mild-mannered janitor. We all bought the dog-as-a-janitor schtick.  But when crime and injustice threatened his neck of the woods, he donned a black mask and a karate outfit and became a martial-arts superhero.

And to our gurgling delight he was bunglingly incompetent. He always managed to mess it up somehow, and still come out smelling of roses. It didn’t matter: he had two distinct personae. When one went wrong he simply became the other.

Alter ego, says The Oxford English Dictionary, can be two things. It can be an intimate friend; or it can be one’s other self.

You would think, wouldn’t you, that one self would be enough for anyone. If Myself is going well, I am the life and soul of the party, and who would want not to be me? And if Myself is going badly I am so wrapped up in my misery, the thought of double that amount of misery is oppressive.

Surely, one of me is enough.

But in our stories we often create alternative realities. Look at Cinderella: it only took a fairy godmother for a drudge to become a princess. The once and future king of all England, Arthur, started out his life as a page. Harry Potter was just a small spectacled schoolboy living under the stairs before he became student wizard and quidditch captain.

Even in this day and age, we go to great lengths to create an ideal version of ourselves. Norma Jean Mortenson became Marilyn Monroe; Archibald Leach was Cary Grant. They chose a name and stepped into the role.

But the new person wasn’t false: it was just part of them. It is possible Cinderella was made a great princess by the time she spent in the scullery, and Arthur never forgot his time as a page, becoming a humbler and fairer king.

All those myths; all those social stories about superheroes and double lives: are they a thin veil over a question which whispers on in the back of our mind?

Because all of us have different sides for different people; different places; different days, even.

Robert Louis Stevenson, in Dr Jekyll and Mr Hyde,  saw a picture in which the two halves in one person were barely one person at all, but separating clearly into two: the good and the evil.

One day he was woken by a friend from a nightmare, screaming. But he was furious with the man who woke him up; because he was dreaming the story of Jekyll and Hyde, and he had been roused at a key moment. He woke just as the transformation scene was about to happen.

There are many apocryphal tales surrounding the creation of this tale of two personalities in one body. One says Stevenson was fired up on cocaine for the duration of his writing the work.

Another claims he worked non-stop for three days to create the first draft, and then burnt the manuscript.

He burnt it, the story goes, because he felt he had not made it enough of an allegory. He had not stressed clearly that this was a tale for Everyman. We all have good inside, his story said, and we all have evil. All either side needs is our permission.

It is a very black and white view of who humans are, created by a man who was clearly in conflict when he wrote it. But what he made was a work of such power it has entertained us, and asked questions of us, for more than a century.

And I wonder if Stevenson, sitting in a writing room in his house, obsessed, half-crazed and elated, is an even better illustration of duality than his book. Because someone who gives all the signs of being unhinged and out of control has bestowed a lasting legacy to the globe.

In each of us sits a rather glorious paradox. Each of us has their alter ego.

And those around us do too. The Oxford Dictionary cannot find a separate word to define the two concepts: of one’s other self; and the intimate friend. Could it be that they are an extension of the same idea?

Mr Rochester thought so. He saw Jane Eyre as his better half, and uttered one of the most seismically romantic lines of all time to his little governess: “I ask you to pass through life at my side – to be my second self, and best earthly companion.”

One’s other self, and best earthly companion.

And so, to my own alter ego.

He has just shambled in from his bath and spotted an etching of John Claire on he television. “Do you think I look like him?” He inquires. He sticks his chin out to show his best side.

I say, who is the man in the etching? Is he Keats? He says I don’t know, but do I look like him? I say, holdonholdon, is he Keats?

Phil says it’s time to stop this conversation because it’s getting too circular.

He has downloaded a morse application on my iPhone. He telephones my father up and plays a string of morse to him, to see if Dad can decipher it before he decides it’s a crank call and hangs up.

Dad passes with flying colours.

Our deaf old cat paces back and forth at his feet, meowing stridently, because she knows he is a soft touch. He has stood selling toys at the christmas fair, all afternoon, commending himself loudly on being a great seller, a consummate marketer of second-hand Postman Pats.

The way he looks still makes my heart miss a beat.

He is very, very like me. He passes through life as my second self.

And my best earthly companion.