Thanos. He’s been in comics for over 40 years. These are his stories, in (somewhat) chronological order.
Iron Man Volume 1 #55 by Mike Friedrich and Jim Starlin. Grade: B
Captain Marvel Volume 1 by Mike Friedrich and Jim Starlin. Grade: A #26-29, 31 (first time he reveals his love of Death), 33 (first “death” of Thanos)
Avengers Volume 1 #118 (Thanos appears in one panel), 125 (Thanos hides behind a chimney)
Marvel Feature #12 (Thanos appears in one page)
Warlock Volume 1 by Jim Starlin #9-16 (first appearance of infinity gems). Grade: A
Avengers Annual #7 by Jim Starlin (death of Warlock). Grade A
Marvel Two-In-One Annual #2 by Jim Starlin (death of Thanos). Grade: A
Logan’s Run #6 (back-up story only) by Scott Edelman and Mike Zeck. Grade: C
Marvel Graphic Novel #1: The Death of Captain
Marvel by Jim Starlin. Here. Grade: A
Silver Surfer Volume 1 by Jim Starlin and Ron Lim. Grade: B+
#34, 35, 36, 37, 38, 44, 45-47 (origin of Mephisto), 49, 50
Thanos Quest by Jim Starlin and Ron Lim. Grade: B+. # 1, 2
Spidey Super Stories (non-canon). Here.
The Infinity Gauntlet by Jim Starlin and George Perez. Crossed over with Grade: A. #1, 2, 3, 4, 5, 6
Tie Ins:Silver Surfer #55; Spider-Man #17
Infinity War by Jim Starlin and Ron Lim. Grade: C+. #1, 2, 3, 4, 5
Warlock and Infinity Watch #9 by Jim Starlin and Angel Medina (Gamora gets upgraded). Grade: B-.
Marvel Comics Presents by Gerry Conway and Scott Kolins (Death speaks to Thanos for the first time). Grade: B-. #109-111
Marvel Holiday Special (1993). Here.
Infinity Crusade by Jim Starlin and Ron Lim (1993). Grade: D. 2-6
Thanos’ appearances from 1993-1996. Grade: F. Here.
Ka-Zar by Mark Waid and Andy Kubert (1998). Grade: F/A (for cornball factor) #7-11
Deadpool #33, 64 (cameos only)
Avengers: Celestial Quest by Steve Englehart and Jorge Santamaria (2001). Grade: B
Infinity: Abyss by Jim Starlin and Al Milgrom (inker) (2002). Grade: B-. Here.
Marvel Universe: The End by Jim Starlin (2003). Grade: A. #1, 2, 3, 4, 6
Jim Starlin and Al Milgrom (inks). Grade: A-. #1, 2, 3, 4, 5, 67, 12
Dan Slott’s Thanos (Great Lakes Avengers X-Mas Special (2005) & She-Hulk #12-13 (2006). Grade: B. Here.
Marvel Adventures Fantastic Four #16 (non-canon, all ages). Grade: D
Annihilation Event (2006). Grade: B-. Here.
Thanos on TV. Here.
Lockjaw and the Pet Avengers (non-canon, all ages). Here
Deadpool #15 (in Pool-O-Vision only).
Avengers and the infinity Gauntlet by Brian Clevinger, Lee Black, and Brian Churilla (all-ages, non-canon) (2010). Grade: A. Here.
Thanos in 2010-2014. Grade: C+. Here.
Thanos today (includes The Infinity Revelation). Grade: B. Here.
Thanos: Relativity (2015). Grade: C+. Here.
Thanos: The Infinity Revelation (2016). Grade: C+. Here.
The Top 15 Thanos Stories of All Time. Here.