|"Is this all real? Or has this been happening inside my head?"
The subject of this article is a real-life person, company, product, or creative work that has been mentioned "in-universe" in a canon source. The Harry Potter Wiki is written from the perspective that all information presented in canon is true (e.g., Hogwarts really exists), and, as such, details contained in this article may differ from real world facts.
Queen of England
When the British Ministry of Magic was begging for recognition and protection under Muggle law, Queen Mary and King William failed to send a delegation to them, which contributed to the introduction of the International Statute of Wizarding Secrecy in 1692. 
The name "Mary" is the usual English form of Maria, which was the Latin form of the New Testament Greek names Μαριαμ (Mariam) and Μαρια (Maria) - the spellings are interchangeable - which were from the Hebrew name מִרְיָם (Miryam). The meaning is not known for certain, but there are several theories including "sea of bitterness", "rebelliousness", and "wished for child". However it was most likely originally an Egyptian name, perhaps derived in part from mry "beloved" or mr "love".
- J.K. Rowling's Official Site (Mentioned only)