Main Characters

• Richard "Rick" Brant - A tall, slim boy of high school age, with light brown hair and brown eyes. Rick gets to help with the scientific experiments and go on expedition all over the world. Rick has a pilot's license and flies his own plane. He is always working a some gadget that oftens helps solve the mystery.
• Donald "Scotty" Scott - Is about Rick's own age, but he had three years of Marine Corps experience behind him. He had talked a recruiting sergeant into believing that he was of enlistment age, and had fought through the South Pacific and Central Pacific campaigns.

Family

• Dr. Hartson William Brant - Rick's father, is an engineer, a Master of Arts, a doctor of science in physics, a member of numerous scientific societies, and a Fellow of the American Institute of Atomic Scientists. He was an able athlete and an ardent fisherman and swimmer. More than once he had been mistaken for Rick's older brother.
• Mrs. Brant - A small, attractive woman with a pleasant face.
• Barbara "Barby" Brant - A slender, blond girl, a year younger than Rick. She always wants in on the adventures.
• Dismal "Diz" - The shaggy little, family dog, whose only trick was to roll over and play dead with all four legs in the air.

Spindrift Scientists

• Professor Hobart Zircon - A huge barrel of a man, over six feet tall, bearded of face with a bushy shock of hair and a voice that shook the walls. He was one of the country's foremost electronic scientists, and almost as famous as Rick's father.
• Professor Julius Weiss - A meek-looking little man with just a fringe of hair on his head, looked more like a clerk or a bookkeeper than a noted mathematician. His undistinguished appearance hid one of the keenest scientific minds in the country.
• John Stringfellow - Fitted his name. He was lean to the point of gauntness, precise of speech and neat of dress. He was a wizard at mathematics and a skilled radio technician.
• Professor John Gordon - A short, stocky man with cropped, gray hair. He was a former Navy officer and an expert on aviation electronics and jet propulsion. He was also a recognized authority in his hobby of archeology.
• Dr. Wisecarver - Designed the rocket fuel for the rocket in The Rocket's Shadow. He simply disappears after The Lost City.
• Dr. Howard Shannon - The staff zoologist, was very tall and very thin. He wore glasses so thick they magnified his eyes - but they were eyes with a twinkle in them and their color was a brilliant blue. His thinning hair was almost white.
• Dr. Anthony "Tony" Briotti - An archeologist with an international reputation. He was of medium height, well-knit, with black hair and a deeply tanned complexion.
• Dr. Parnell Winston - A cyberneticist, he was a powerfully built six-footer with a heavy thatch of thick black hair and amazingly bushy eyebrows. His face was ruddy. He was forty, but looked ten years younger.
• Dr. Walter Miller - A physicist was a tall man with a kind, tired face, steel-rimmed glasses, and a shock of curly white hair.

Locals

• Jerry Webster - A reporter for the Whiteside, New Jersey newspaper, The Morning Record.
• Duke Barrows Editor of The Morning Record. Jerry's boss.
• Gus - Manager of the Whiteside Airport, gasoline attendant, mechanic, flight instructor and philosopher. Gus was only about three years older than Rick.
• Mr. Huggins - Ran the farm on the island that supplied food for the Spindrifters
• Cap'n Mike - Captain Michael Aloysius Kevin O'Shannon, 70 year old former fisherman. Lives in a shack outside of Seaford near Smugglers' Reef.

Others

• Chahda - Was a former Bombay beggar boy who had become a member of the Spindrift family by virtue of his courage and loyalty when the scientists sent an expedition to Tibet to set up a radar moon relay station. In Bombay the Hindu boy had tried to educate himself by memorizing most of an old copy of the "Worrold Alm-in-ack", as he called it.
• Dr. Paul Warren - Tall with a neat, brown beard. He was the head of the Pacific Ethnographic Society and an old friend of Hartson Brant.
• Steve Ames - The young intelligence office of JANIG, the secret Joint Army-Navy Intelligence Group, which was charged with protecting the security of American government secrets.
• Mike Curtis - Private detective who is involved in some of the boys adventures.
• Captain Ed Douglas - of the New Jersey state police.
• Janice "Jan" Virginia Miller - The daughter of Dr. Miller. A remarkably pretty girl, as dark as Barby was fair, and of about the same height and slimness.

Ships

They're not really characters but ships, boats and submersibles have played keys roles in many of the adventures.

• John S. Madigan - Freighter that the boys sailed on to get to India in The Lost City.
• Tarpon - Converted fishing trawler used in 100 Fathoms Under and The Phantom Shark
• Submobile - Tethered submersible invented at Spindrift Island in 100 Fathoms Under.
• SS Aloha - Ship that brought Zircon and the Submobile to Hawaii in 100 Fathoms Under
• Asamo - Japanese cruiser sunk by the Dutch that held treasure plundered during WWII in 100 Fathoms Under.
• Eleanor II - 30 foot cabin cruiser on which Steve Ames first came to Spindrift in The Whispering Bo Mystery.
• Kookaburra - The Australian Kenwood's schooner in The Phantom Shark.
• Sea Belle - Tom Tyler's fishing boat that ran aground on Smugglers' Reef.
• Albatross - Brad Marbek's fishing boat in Smugglers' Reef.
• Jennie Lake - Bill Lake's fishing boat in Smugglers' Reef.
• Asiatic Dream - Freighter that the boys sailed on to get to the Philippines in The Golden Skull.
• Water Witch - Boat used by the boys in The Wailing Octopus
• Maiden Hand - The bark sunk by the pirate Anne Bonney that the boys are looking for in The Wailing Octopus.
• Sampaguita - Thirty-foot auxiliary sloop that Briotti and Shannon rented in the Philippines in The Pirates of Shan.
• Swift Arrow - Converted motor torpedo boat that the boys rented to look for Briotti and Shannon in The Pirates of Shan.
• Spindrift - Originally the bad guys houseboat in The Electronic Mind Reader, Rick bought it at a government auction. Rick and Scotty use it to take a vacation to the Chesapeake Bay in The Flying Stingaree.
• Kingsport - Satellite tracking ship in The Veiled Raiders.
• Sea Horse - Deep sea submersible in Danger Below!
• Sea Beast - Tender ship for the Sea Horse in Danger Below!
• Hester II - Tug boat that lost the drilling rig in Danger Below!