A road bicycle racer who works for the benefit of his team and leader often at the expense of his/her own individual performance. The workhorses of the teams, these cyclists have the job of doing anything possible to help their team leader perform well. This can even mean sacrificing your own bike or wheels if your team leader has a crash or puncture.
The French "domestique" translates as "servant". The word was coined in 1911, although such riders had existed before then.