Ada Lovelace was born Ada Byron in 1815. Though she never met him, Ada was the daughter of the poet Lord Byron.
In 1833 (when she was only 17), Ada met Charles Babbage, the inventor of the Difference Engine. They became lifelong friends, and later, scientific collaborators.
In 1835, Ada married William King, who subsequently inherited a noble title, whereupon Ada became "Ada Byron, Countess of Lovelace."
Babbage enlisted the Countess's help in translating the memoir of an Italian mathematician, and in the process Ada produced copious notes of Babbage's Difference Engine. It is for these documents, simply titled "Notes," that she remains famous today (although probably less so than she deserves). Although she is credited as the "founder of scientific computing," I would also argue that Ada was the first technical writer. ;-)
Ada Lovelace died of cancer in 1852.