A nursery rhyme, relating to the Wild Hunt, where Arthur O'Bower rides on the wind, personifying a storm. The Arthur in question is indeed King Arthur, who has broken his band--the Knights of the Round Table--while he fought the son of the king of Lothain (part of Scotland)--Mordred.

It is also popularized from Beatrix Potter's The Tale of Squirrel Nutkin.

A bower can either be a cottage, a woman's boudior, an anchor, or a Fool; as Harlequin is identified as leader of the Wild Hunt in France, this last one may be applicable.

I have also seen that bower may be a confusion with bowder, meaning "a blast or squall of wind."

Parallels:

The great Bull of Bendy-law
Has broken his band and run awa
And the king and a' his court
Canna turn that bull about.

--from Scott's Border Minstrelsy

Or:

In Nottingham there lives a jolly Tanner
His name is Arthur a Bland:
There is ne're a 'Squire in Nottinghamshire
Dar bid bold Arthur stand

Robin Hood and the Tanner