There is no official commercial Blu-ray player for Linux.
Linux users have to use open-source libraries capable of handling the DRM schemes that protect these disc contents. This is legal in most countries where interoperability allows this.
The Arch Wiki provides a very good article which explains the background, including detailed steps on how to watch Blu-ray disks with DRM.
The most comprehensive source of public VUKs available is fvonline-db.bplaced.net. Personally, I prefer to use VLC for any kind of media playback, but there are other open-source player available as well.
The law of my country (Germany) permits to make use such open-source libraries, which is also the case in the majority of foreign countries. Nevertheless, you should check if it is legal in your country to overcome DRM for the purpose of watching movies.