Rain's years of training in the Special Forces, CIA, and as an assassin for hire manifest themselves in a deep-seated paranoia, an inability to trust anyone, and the drive to eliminate any loose ends (usually through killing) that may leave him vulnerable to payback or revenge.
He has undergone plastic surgery to hide his European heritage and has dyed his brown hair.
In 1960, Rain's father was killed, so his mother moved them to Dryden, NY where she taught at Cornell.
He is also a Vietnam veteran where he served with the US Army Special Forces and had his first encounter with the CIA that later led to his recruitment.
Afterwards, he worked for the Japanese LDP, unwittingly for Yamaoto (a local powermonger) and Holtzer (a rogue CIA operative, later killed by Rain himself).
The character is featured in Rain Fall a 2009 major motion picture directed by Max Mannix and starring Kippei Shiina and Gary Oldman.
His 2½ year old son, the result of a night with Midori Kawamura, a jazz pianist, who was the daughter of one of Rain's targets.
Built like a linebacker and originally sporting a goatee, Dox and Rain have formed a deep friendship, the former having turned down a chance at five million dollars in favor of helping the latter, who was badly wounded.
Dox speaks with a Southern twang, and masks a deadly persona with an "aw shucks" attitude.
Her profession with the Mossad is to seduce potential terrorists and gather information about them, to enable their assassinations.
Rain got to know her as their paths crossed when he had the task to eliminate an arms dealer in Macau, who was also Delilah's target.
"Harry", is a former NSA employee who was born in America and went to college and graduate school there, earning a degree in applied mathematics and cryptology.
Rain's unwitting partner, Harry didn't know his employer's true profession—and never asked.
Harry was the classic otaku – and, in addition to being a computer guru – was a guy who has saved Rain's life countless times by equipping him with the latest gadgetry.
In the second book, he fell in love with a Japanese hostess who showed herself to be an "agent" of Yamaoto's criminal organization, hired to track John Rain's location.
Jim Calhoun, a childhood friend who Rain was forced to kill in Vietnam despite his better judgment.
An ex-CIA operative, Non-official Cover, former financial planner based in Hong Kong.
Unlike the other enemies, Hilger does not act because of seeking personal gain but out of a sense of patriotism.
He used them hoping to draw Rain out of hiding; this however backfired causing only Yamaoto's death.