Grove Online is the big daddy of classical music resources (at least in English). Its origins rest with one of the crazy 19th century encyclopedists, George Grove, who was asked to write a musical dictionary for amateurs.
Over the years it grew to a hefty twenty plus volumes, and is now the authoritative source, available online for a fairly sizeable subscription (although many academic and some public libraries offer access for card holders.) It combines “life and works” info, including musicological and interpretive music history context where relevant, and there are multimedia examples you can play or pull into programs like Sibelius. They are trying to deal with the question of how you update a professionally written and edited (rather than crowd-sourced) encyclopedia. Not completely up-to-date: Did just check and they still have Peter Maxwell Davies as the Master of the Queen’s Music (it’s Judith Weir now). So best to combine with other resources, but still the place to go for things like a comprehensive summary of the history of the mass in Western Classical music.
And on a lighter note, here’s Dame Kiri in a favorite encore of hers, “Art is Calling For Me,” which I heard the next rising star, Pretty Yende sing in a wonderful recital recently.
Best line “I want to be want to be a screechy peachy cantatrice.” Neither Pretty, nor Kiri have the least bit screechy about them! Only truly great singers can bring this one off..