The wrap is most likely vinyl though there is a possibility, leather. This is probably dirt, grime and body oils from folks hands. If you or a previous owner were smokers, it will be worse and probably impossible to clean completely. As far as cleaning, try a leather cleaner first and get stronger if necessary. My experience is that you can get much of it off, but it will never come totally clean, leaving residual grime and shiny areas near the spokes where people hook their fingers.