The original Silver Age series ran 80 issues, from December 1956 to October 1966. In additional to anthological stories, several issues featured the adventures of modern-dress sorcerer Mark Merlin. The dual-personality Eclipso ("Hero and Villain in One Man!") was introduced in issue #61 (Aug. 1963), continuing to the series' end. Prince Ra-Man the Mind-Master bowed in #73 (Oct. 1965) (later retconned into being the same person as Mark Merlin). Other, lesser continuing features included "Peter Puptent, Explorer"; "Dolly and the Professor"; "Doctor Rocket"; and "Moolah the Mystic".
The series was revived three years later with a definite article as The House of Secrets, beginning with issue #81 (Sept. 1969). Now its horror and suspense tales were introduced by a host named Abel, who would also host the satirical comic Plop! and later become a recurring character in The Sandman (and related series such as The Dreaming). His brother Cain hosted House of Mystery.
The House of Secrets is also the name of the actual edifice in which Abel lives. Mike Friedrich (writer) and Jerry Grandenetti (artist) introduced the house and explained its origins. The Sandman series revealed it exists both in the real world of the DC Universe and in the Dreaming, as a repository for secrets of all kinds.
The building itself was constructed for a Senator Sanderson using only materials from Kentucky, and went under the enchantment that only pure-blood Kentuckians would be able to live there. Later, Sanderson's wife went insane in the upper floors, leading the Senator to sell the house. The next four owners, none of them pure Kentuckians, found themselves driven away for various reasons. The following owner attempted to move the home from its original location, but the house tore itself free from its trailer, ran its owner over a cliff to his death, and settled less than 200 yards from the Kentucky state line in a graveyard. Whether by fate or some mystical alignment, the companion House of Mystery stands at the other end of the graveyard. Shortly after this, Abel was driven to the house and entrusted as its caretaker by a man who revealed himself to be an aspect of the House's existence, but making vague references to an employer.
This revival, sporting many covers by Neal Adams, Bernie Wrightson and Mike Kaluta, ran through issue #154 (Nov. 1978), with three months passing between #140 (April 1976) and #141 (July 1976), a victim of the DC Implosion. It was then 'merged' into The Unexpected with issue #189.
The enduring character Swamp Thing was introduced in #92 (July 1971).