Royal Caribbean International was founded in 1968 by a consortium of three Norwegian shipping companies: Anders Wilhelmsen & Co, I. M. Skange & Co., and (later) Gotaas Larson. Wilhelmsen later took over sole ownership, then turned the line into a joint venture with the owners of the Hyatt hotel chain and the shipowning Ofer family. Royal Caribbean operates 19 ships ranging from about 50,000 to over 135,000 tons, each carrying from 2,000 to 3,000 passengers. Its destinations are in the Caribbean, Mediterranean, North Sea, Alaska, and Hawaii. The flag is white with the company logo, a crowned anchor, in dark blue.
Anders Wilhelmsen & Co houseflag: Diagonally red over blue from lower hoist to upper fly with a white W in the centre. The other companies should be I. M. Skaugen & Co. (seehouseflag) and Gotaas-Larsen (houseflag yet unknown).
Their Norwegian language web site says the company now operates 29 ships.
I think the company is based in the US nowadays, though there is an office in Oslo as well. Anyway, finding out how to attribute nationality to shipping companies these days is rather difficult with ships registered under one or more flags and with ownership from several countries, etc.