Thomas Wickham Prosch (1850-1915), the son of pioneer parents Charles and Susan Prosch, moved with his family from Brooklyn, New York, to the Pacific Coast in 1855. Charles Prosch was a printer and, in 1858, founded the in Steilacoom. Thomas Prosch helped his father with the newspaper from an early age, and also worked as a salesman and as a hand at a logging camp. He also worked as a clerk in the State legislature when he was nineteen and, one year later, began work at the customs office at Port Townsend.

In 1867, Charles Prosch and two of his sons, Thomas and Fred, acquired the from Randall H. Hewitt and continued its publication in Olympia. By 1872, the newspaper had endured many financial difficulties; however, Thomas was able to purchase complete ownership of the paper. In 1873 he moved to Tacoma, where he continued publication of the paper until 1875, when he—and the paper—relocated to Seattle until it ceased publication in 1878.

One year later, in 1879, Prosch and Samuel L. Crawford purchased the , a Seattle newspaper. In 1881, that paper merged with the to become the . After becoming the sole owner in 1884, early in 1886 Prosch sold the paper to a joint stock company.

Prosch was also deeply involved in Seattle affairs in many other ways. In 1876, he was appointed postmaster of Seattle by President Grant, and held that post for the next two years. He also had charge of the municipal census of Seattle in 1890 and, at the same time, was the special agent in charge of the federal census in Seattle. In the early 1890s, he served for three years as a member of the Seattle School Board. In 1894, he aided in platting the tidelands of Seattle and Tacoma. Prosch was also active in the Seattle Chamber of Commerce (serving as secretary for three years and as a member of the board of trustees for fourteen), and was a member and officer of many different pioneer and historical societies, including the Washington Pioneer's Association.

Much of Prosch’s later life was devoted to historical writing and collecting. He wrote many books about the history of the Puget Sound region, including , , and . He also wrote many articles for the .

In 1877, Prosch married Virginia McCarver, who was the daughter of Morton and Julia Ann McCarver, the founders of Tacoma. They had six children: Julia, Edith, Genevieve, Beatrice, Phoebe, and Arthur. Thomas and Virginia both died on March 30, 1915, when the car in which they were passengers fell from the Riverton Draw Bridge into the Duwamish River.