|This page in a nutshell: No one "owns" content (including articles or any page at Wikipedia). If you create or edit an article, other editors can make changes, and you cannot prevent them from doing so. In addition, you should not undo their edits without good reason. Disagreements should be calmly resolved, starting with a discussion on the article talk page.
All Wikipedia pages and articles are edited collaboratively by the Wikipedian community of volunteer contributors. No one, no matter what, has the right to act as though they are the owner of a particular article (or any part of it). Even a subject of an article, be that a person or organization, does not own the article, nor has any right to dictate what the article may or may not say.
Some contributors feel possessive about material they have contributed to Wikipedia. A few editors will even defend such material against others. It is quite reasonable to take an interest in an article on a topic you care about—perhaps you are an expert, or perhaps it is just your hobby; however, if this watchfulness starts to become possessiveness, then you are overdoing it. Believing that an article has an owner of this sort is a common mistake people make on Wikipedia.
Once you have posted it to Wikipedia, you cannot stop anyone from editing text you have written. As each edit page clearly states:
Work submitted to Wikipedia can be edited, used, and redistributed by anyone
Similarly, by submitting your ideas (for article organization, categorization, style, standards, etc.) to Wikipedia, you allow others to challenge and develop them.
If you find yourself in an edit war with other contributors, why not take some time off from the editing process? Taking yourself out of the equation can cool things off considerably. Take a fresh look a week or two later. Or, if someone else is claiming "ownership" of a page, you can bring it up on the associated talk page, appeal to other contributors, or consider the dispute resolution process.
Even though editors can never "own" an article, it is important to respect the work and ideas of your fellow contributors. Therefore, be cautious when removing or rewriting large amounts of content, particularly if this content was written by one editor; it is more effective to try to work with the editor than against them—even if you think they are acting as if they "own" the article. (See also Wikipedia:Civility, Wikipedia:Etiquette, and Wikipedia:Assume good faith.)
Being the primary or sole editor of an article does not constitute ownership, provided that contributions and input from fellow editors are not ignored or immediately disregarded. Editors familiar with the topic and in possession of relevant reliable sources may have watchlisted such articles and may discuss or amend others' edits. This too does not equal ownership, provided it does not marginalise the valid opinions of others and is adequately justified. Often these editors can be approached and may offer assistance to those unfamiliar with the article.