Elvis Costello: King Horse

Cafe Society
1

“Now I know that you’re all King Horse, between tenderness and brute force”

This is one of my favorite Elvis Costello songs but I just can’t figure out what the term “King Horse” is supposed to mean. I’ve tried to figure it out from context but it seems the term is used as if it is meant to be a familiar expression to the audience.

Is E.C. using imagery of his own invention and simply failing to get his point across to me?

Or, is this a vernacular expression that predates E.C.'s use?

Is it that it’s a British expression unfamiliar to my American ears?

Most importantly: WHAT DOES IT MEAN?

2

He says in the sleeve notes to the remastered Get Happy that it is about ‘a very famous rock star’ and his way of dealing with fame - ie to believe the hype.
In a recent interview in the Guardian newspaper he said it was Springsteen and that it made him determined to react differently to any fame he may experience.
King Horse is not a common British expression, but I took it to be similar to the expression ‘cock of the walk’ - meaning a creature who was conspicuously in charge.
I think you can access the interview at www.guardianunlimited.co.uk

Cheese