[The Australian Panther]

The Who - Happy Jack - LIVE (1967)
https:www.youtube.com/watch?v=h_qgrG_ZxEY&ab_channel=Beat-Club

This Happy Jack was a Donkey, I think 'Jack' was US slang for Donkey.
[He lived in the sand at the Isle of Men
The kids would all sing, he would take the wrong key
So they rode on his head on their furry donkey

The kids couldn't hurt Jack
They tried and tried and tried
They dropped things on his back
And lied and lied and lied and lied and lied

But they couldn't stop Jack, or the waters lapping
And they couldn't prevent Jack from feeling happy]
Great Rock song, great lyrics.

Link to the book: Happy Jack 2

[Robb_K]

This Happy Jack was a Donkey, I think 'Jack' was US slang for Donkey.

I've never heard of "Jack" being a US slang word for donkey.  The Who were a British group, in any case.  And I also never heard "Jack" used as slang for donkey in The UK.  Maybe they named it after the comic book character, after seeing this US book a sailor brought to The UK???

But, Happy Jack was really EC's Handy Andy, from their 1946-47 "Dandy Comics" series.  This book was a hodgepodge collection of low-cost stories from various unrelated defunct publishers, from gathered old printing plates bought at warehouse and printing plant stock clearing sales by Robert Farrell of Ajax-Farrell Publishing, for their Decker/Red Top reprint series.

[crashryan]

The explanation of the Who song that I'd always heard is the one given in the Wikipedia entry:

According to some sources, Townshend reported the song is about a man who slept on the beach near where Townshend vacationed as a child. Children on the beach would laugh at the man and once buried him in the sand. However, the man never seemed to mind and only smiled in response.

From a long bout of Googling I concluded that no one seems to know what the "official" lyrics are. Especially the "furry donkey." Some say that this is a reference to donkey rides which were supposedly popular in UK seaside towns. It's unclear whether they're saying the cruel kids "rode" on Jack physically, which seems unlikely no matter how patient Jack was.  Personally I thought this analysis made more sense:

Everyone thinks the lyric is "furry donkey" (on ALL of the lyrics sites), but that makes as much sense as the Jimi Hendrix lyric "scuze me while I kiss this guy." Just listen to it and you'll hear a lyric that makes perfect sense: "They rode on ahead in a hurry on Quay." Note the Quay is pronounced "Key" and it is the main road along the beach on the East side of he Isle of Man. It is quite clear that this is the correct lyric."

But then the writer goes on to question the water lapping, and he loses me:

I also wonder about the line "They couldn't stop Jack or the water's lapping", as it makes more sense as "They couldn't stop Jack or thwart his laughing." The latter line makes perfect sense in light of the song's theme. However it does sound more like "lapping" but that could be due to the liquor or pot in Roger's system when he was singing it.

[The Australian Panther]

https://www.quirkyscience.com/donkeys-burros-mules/

  And a Jackass
So a jackass is an irritating human, right? Well, a male donkey is called a jack and a female is a jenny or a jennet. Hence, a jack-ass (or jackass) is a male donkey.   

https://songmeanings.com/songs/view/11609/

Happy Jack wasn't old, but he was a man
He lived in the sand at the Isle of Man
The kids would all sing, he would take the wrong key
So they rode on his head on their furry donkey 

That makes it clear that Jack was actually a man who a group of children 'rode like a donkey'
That makes the whole song quite clear, except for the line about
'But they couldn't stop Jack, or the waters lapping'
For me that's just the poet in Townsend coming out, an image emphasizing how difficult it would have been to stop Jack being happy.
I feel this song is from Townsend's memory of something he witnessed. The description of the children's behavior, without malice, is dead accurate.
I have witnessed this kind of thing from children several times.
To me its a very exuberant happy song. Joyful, playful, fun.
the tune gives emphasis to the image created by the lyrics.   
Really a very clever song.
cheers!