Here are the h-i authors.
Steven Hahn - Mindwipe!
Isidore Haiblum - The Identity Plunderers
Jack Haldeman II - Vector Analysis
Joe Haldeman - The Forever War
Edmond Hamilton - Starwolf
Karl Hansen - War Games
Charles Harness - Firebird
Harry Harrison - all of them
Kenneth Hassler - Intergalac Agent
Simon Hawke - all of them
Ward Hawkins - Red Flame Burning
H.F. Heard - Doppelgangers
Robert Heinlein - all of them
Zenna Henderson - The People No Different Flesh
Frank Herbert - The Santaroga Barrier, Hellstrom's Hive
Phillip High - The Time Mercenaries
P.C. Hodgell - God Stalk
James Hogan - all of them
Joan Hunter Holly - The Time Twisters
H.M. Hoover - Return To Earth
Robert Hoskins - To Control The Stars
Robert E. Howard - Wolfshead
Fred Hoyle - October The First Is Too Late
Hoyle & Hoyle - The Incandescent Ones
Trevor Hoyle - Through the Eye Of Time
L. Ron Hubbard - Slaves Of Sleep
Edward Hughes - The Long Mynd
Zach Hughes - all of them
Dean Ing - all of them