Dr. Mauve

William Perkin, inventor of mauve dye.

Introduction to How Common Is Accidental Invention? by Brian Potter:

One of the most important inventions of the 19th century was mauve dye, the first synthetic aniline dye. First synthesized by William Perkin in 1856 out of coal tar, mauve led to the creation of an entire synthetic dye industry. Within a few years, many other aniline dyes, such as magenta, aniline blue, aniline yellow, and aniline black had been discovered, and large industrial operations had sprung up to manufacture them. The synthetic dye industry ultimately evolved into the industrial chemical industry in the late 19th century (using coal and coal-tar as its primary feedstock). Synthetic die manufacturing was also the industry where the first industrial R&D labs appeared, formed to uncover new chemical knowledge in service of creating better and more efficient dyes and dyeing processes.

He goes on to discuss a number of 'accidental' inventions.