linux - difference between adduser and useradd

What's the difference between “adduser” and “useradd”?

I wonder: Why are there these two commands on Debian Linux, with very similar names and functionality? This has always been confusing for me.

• Is any of them superior to another?
• Why aren't they merged into one?
• Is there any significant difference between them?
• Which one should I use? Or does it depend on a use case?

useradd is native binary compiled with the system. But, adduser is a perl script which uses useradd binary in back-end.

adduser is more user friendly and interactive than its back-end useradd. There's no difference in features provided.

source - http://superuser.com/questions/547966/whats-the-difference-between-adduser-and-useradd