Before there was a Marvel Comics Publishing house, there was a company called Timely Publications. The very first comic they produced in October 1939, Marvel Comics #1 would star The Human Torch, Namor The Submariner, the Angel and Ka-zar the Jungle lord.
Later, they would change their name to Timely Comics and publish more well known characters such as Captain America and his sidekick, Bucky. Eventually, in 1961, Timely Comics because Marvel comics and we know how well that turned out.
Due to the historical nature of Timely Comics, I felt it was worth keeping an eye out for any 1st Appearances.
1ST APPEARANCE OF STEVEN UNIVERSE IN COMICS ADVENTURE TIME 2013 SPOOKTACULAR
Time Remaining: 22h 41m
Buy It Now for only: $11.99
Adventure Time Spooktacular 1 VF NM 1st Appearance Steven Universe
Time Remaining: 10d 1h 43m
Buy It Now for only: $14.99
KURT BUSIEKS ASTRO CITY NO1 2 ALEX ROSS COVER 1ST APPEARANCE OF TIME KEEPER
Time Remaining: 13d 2h 45m
Buy It Now for only: $1.25
ADVENTURE TIME WITH FINN AND JAKE 1 1ST PRINT COVER C VARIANT 1ST APPEARANCE
Time Remaining: 13d 19h 3m
Buy It Now for only: $35.00
1ST APPEARANCE OF ADVENTURE TIME WITH FINN JAKE IN COMICS RARE FCBD
Time Remaining: 14d 6h 19m
Buy It Now for only: $20.99
ARCHER ARMSTRONG 8 1ST APPEARANCE IVAR THE TIME TRAVELER
Time Remaining: 18d 12h 13m
Buy It Now for only: $10.49
Captain America Out of Time Issues 1 6 1st APPEARANCE OF WINTER SOLDIER
Time Remaining: 29d 6h 16m
Buy It Now for only: $50.00