From SFWiki

Coit Tower was dedicated in 1933 and sits at the top of Telegraph Hill where the west coast's first telegraph was constructed in 1849.

It is named in honor of Lillie Hitchcock-Coit who willed one third of her estate to San Francisco to, in her own words "to be expended in an appropriate manner for the purpose of adding to the beauty of the city which I have always loved."

The myths that Coit Tower was meant to resemble the nozzle of a fire hose and was dedicated to firefighters are (almost unfortunately) not true. There is however a statue of three firefighters in Washington Square Park dedicated as memorial to firefighters who've lost their lives saving others.