Merck is a research-driven pharmaceutical company with deep roots in oncology, vaccines and infectious disease. Its immunotherapy franchise transformed cancer treatment and the company's finances, while Gardasil protects against HPV-related cancers worldwide. An animal health division adds steady, less cyclical revenue. Merck spends heavily on research and licensing deals to refill its pipeline, a constant necessity in an industry where every blockbuster eventually loses patent protection. The US company traces its history to 1891.