The only Valerian I know 5029, is the Red Valerian wildflower - much loved by the Hummingbird Hawkmoth. Can't say I've ever sniffed it, but I have a feeling that the sleeping drug valium is derived from this plant - someone is bound to know the correct answer.
In Greek, the plant extract valerian was, apparently, called 'phu', which makes the bad-smell idea pretty plain! It has been called 'the valium of the 19th century', but has no chemical connection with that drug. For everything you could hope to know about valerian - but maybe not precisely what makes it smell so badly - click http://www.egregore.com/herbs/valerian.html
Once there, just click on the various headings offered.