Adventures into the Unknown has the distinction of being the first ongoing horror comic title. It lasted for 167 issues from Fall 1948 to August 1967. I remember reading a lot of issues when I was a kid.
Issue #1 is a Pre-Code dandy and has five --count 'em, five -- stories scripted by Frank Belknap Long. (Long was a good friend of H. P. Lovecraft and had a seven-decade distinguished career writing in the horror field. He received Lifetime Achievement Awards from both the Horror Writers Association and the World Fantasy convention.) Notable in this issue is Long's 7-page adaptation of Horace Walpole's classic gothic novel The Castle of Otranto.