In general, a democratic reformer is one who attempts to change a country's policies or laws in order to improve the implementation of democratic ideals. This includes spreading voting rights and fighting for civil liberties.
Anyone who attempts to make systematic changes that allow for a more democratic society can be called a democratic reformer. One example of a democratic reform would be the expansion of voting rights for politicians in China. Since voting is a basic principle of democracy, and a reform would increase the number of people who are able to participate in government actions, it is a democratic reform.