1. In old coal driven steamer ships. The workforce below decks, that shovelled coal into the furnace, to keep the engines going.
2. Reference to Lois McMaster Bujold's Vorkosigan series of scifi books.
In Mirror Dance the character Mark Vorkosigan, clone brother of the series' protagonist Lord Miles Vorkosigan/Admiral Miles Naismith, succums to cumaltive effect of half a childhood of mental conditioning and several days of torture at the hands of a very creative madman. The effect is a type of schizophrenia. He creates several personalities, each with a specialty, to endure his torture sessions and protect his real personality. After he escapes his captivity with their help, he undergoes treatment to control and subdue his 'black gang'.