Some would posit that Ruby would not be a "thing" today without Rails. It would still exist, of course (as it existed way before Rails), but it would probably be a minor language with low adoption, possibly even a language regarded as a learning system rather than one with real-world application.The answer to your question is a definite yes, but there is another question that can be asked: "After learning Ruby, should you learn Rails?", and as for the first question, the answer is yes. Ruby is a great high level language, and the Rails framework adds great value to Ruby.
Personally, I like using Ruby for day-to-day tasks. I think it beats the hell out of Perl as far as language syntax and structures go. On the other hand, I really don't like Rails all that much. Too much "magic" that sometimes causes issues that can...