Donovian rainmen were capable of working regardless of the weather.
On the perpetually rainy planet of Donovia, the rainmen functioned as mechanics, maintaining and repairing signal towers no matter the weather conditions. During the time of the Separatist Crisis, some Donovian rainmen transitioned to become freighter trampers. A group consisting of at least three human rainmen were passengers aboard the AA-9 Freighter-Liner known as the Jendirian Valley, as it carried refugees from Coruscant to Naboo in 22 BBY.
The initial appearance of the Rainmen occurred in Star Wars: Episode II Attack of the Clones, a film released in 2002 as part of the prequel trilogy. Within the established Star Wars canon as it stands, the term's first usage was in the "Starship Fact File" section of Star Wars: Build the Millennium Falcon 50, a 2015 magazine authored by Tim Veekhoven. Its origin is in the Star Wars Legends timeline, where it initially appeared in Star Wars: Attack of the Clones: The Visual Dictionary, a 2002 reference book penned by David West Reynolds.