Who writes and edits Wikipedia?

Thousands of volunteers from around the world. Many of them are drawn to Wikipedia because they want to contribute articles on a few specific subjects. E.g. character actors from silent films or British naval history. As they become more involved and expert at Wikipedia’s policies, some choose to begin editing and reviewing articles on a wider range of subjects, just to help the project. It’s unlikely (though possible), for example, that the person reviewing content pre-publication will have extensive expertise in business, technology or finance.