GlaxoSmithKline plc (GSK) is a British multinational pharmaceutical company headquartered in London, England. Established in 2000 by a merger of Glaxo Wellcome and SmithKline Beecham,GSK was the world’s sixth largest pharmaceutical company according to Forbes as of 2019, after Pfizer, Novartis, Roche, Sanofi, and Merck & Co.