It seems that if your name is Jim, someone’s going to call you “Jimbo” at some point in your life. Why do we have “Jimbo” and not “Johnbo”? Who was the original Jimbo?
You’d think I would know this. But you’d be wrong.
BTW, there IS a guy I call “johnbo”.
My personal theory is that it is rhe result of the combined nicknames of a person named James Robert, hence Jim Bob. Jimbo is a logical extension, at least with my friend Jimmy, who sometimes is known as Jimbo.
Actually, I thought that the “bo” part might come from “boy”.
I have a vested interest in learning this answer.
But I really don’t know myself.
My guess is it’s an alteration of Jumbo, an elephant exhibited by Barnum in 1883. (That in turn may be from Mumbo Jumbo, “a masked figure among Mandingo peoples of western Africa.”)
A section of Debussy’s “Children’s Corner Suite” from 1908 is titled “Jimbo’s Lullaby”. Jimbo was a toy elephant of his daughter, Claude-Emma, whose nickname was Chou-Chou. The suite is dedicated to her.
I think the shortening of “boy” is the answer. Hence, you not only get Jimbo, but Sambo. “Jim” and “Sam” both being popular slave names, I am guessing the Jimbo and Sambo were both originally diminutives of Jim and Sam, used to refer to slave children with those names.