I know it means that you are “ready” to do something, but what does the “brother” part mean?
A play on words, suggesting a whimsical mis-identification
“Are you ready?”
“No, I’m Ready’s brother.”
For kicks I’ve just tried to trace it and can find this mentioning its use in that exact way by Gertrude Stein in 1923.
But its use goes back before that in this 1910 ad:
Maybe someone else can trace farther back than that? I read it as similar to “Danger? Danger’s my middle name.”
I have always taken it to mean I could not possibly be more ready than I am right now.
Could it be a play on the common response ‘I was born ready!’ ?
(does ‘born ready’ go back as far as DSeid’s cite?)
Google Ngram indicates an increasing number of uses of “I was born ready” since the mid-1960’s. Aside from some cases where those words appear together just at random, there’s one earlier use of the sentence. This was in 1929 in the story “Dudley and Gilderoy: A Nonsense” by Algernon Blackwood. I suspect that the sentence was only used in a few social circles before the mid-1960’s and only at that point became well known.
+3
I’m not Ready, but I’m close to Ready.
Yes, it sounds like it mean’s “nearly ready” as Dr. Drake points out. Compare this to the use of “mama” as in a line I once read in a book from the 70’s: “He had dope’s mama!” meaning a lot of dope.
Hmmm. I thought Ready’s brother was Rough…

Hmmm. I thought Ready’s brother was Rough…
Same thought here.
I’m Ready’s sister’s neighbor’s ex-boyfriends former mailman. What does that make you?

Same thought here.
Me too.