Maybe so, but he co-wrote it with Stern.

Rama-Tut/Kang?Immortus has a very convoluted history (it seems to be the nature of the beast for comic book characters, but time travelers in particular), so once again, my Kang timeline -

PHARAOH RAMA-TUT/KANG/IMMORTUS TIMELINE

NATHANIEL RICHARDS [31st century AD] - From Fantastic Four v1 #19 - Rama-Tut revealed that his ancestor (Nathaniel Richards) uncovered an ancestor's plans for a time machine which he built to travel into the past to reign as Pharaoh Rama-Tut

IRON LAD [31st century AD to 21st century AD] - From Young Avengers v1 #1 - Kang traveled into the past to confront his younger self who had gone into the past and affected the timeline.

NATHANIEL RICHARDS [31st century AD] - Apparently Iron Lad returned to his time and the timeline was restored [an obvious conflict with how time travel has been show in the marvel universe]

PHARAOH RAMA-TUT [2950 BC] - From Fantastic Four v1 #19 - Bored with the 31st century, Nathaniel Richards uses the time sphere to travel to ancient Egypt to become Pharaoh Rama-Tut

SCARLET CENTURION [alternate timeline] - From Avengers Annual v1 #2 - Pharaoh Rama-Tut is diverted to the modern era where he encounters Doctor Doom, and takes on the identity of the Scarlet Centurion

KANG THE CONQUEROR [40th century] - From Avengers v1 #8 - In an attempt to return to his time, Pharaoh Rama-Tut is thrown by a temporal disruption into the 40th century, where he takes on the identity of Kang the Conqueror, and he conquers the 40th century earth

VICTOR TIMELY [early 20th century] - From Avengers Annual v1 #21 - established himself in Timely, Wisconsin as an industrialist/inventor, setting the technological advancements into motion that would culminate in the creation of advanced technology such as the golden age Human Torch

KANG THE CONQUEROR [40th century] - From Avengers v1 #23 - Kang eventually returned to the future and ultimately undertook a campaign to abduct the Celestial Madonna [Mantis] to make her his mate. After that plan failed Kang returned to the 40th century where he began eliminating divergent Kangs from the time stream. Eventually, the "Prime Kang" returned to his base, Chronopolis, where, with the help of Libra and some of the Avengers, successfuly broke the link between himself and his future self, Immortus

PHARAOH RAMA-TUT [ancient Egypt] - From Avengers v1 #129 - Returned to ancient Egypt as Pharaoh Rama-Tut where he reigned for a second time

IMMORTUS [master of Limbo] - From Avengers v1 #9 - After the period as Pharaoh Rama-Tut, Kang took on the identity of Immortus, and became the master of Limbo. Immortus on several occassions saught to manipulate the Avengers and his younger self to his own ends, but Kang defeated Immortus using the forever crystal to diverge his future from his apparent destiny of becoming Immortus

Nathaniel Richards [31st century] --> Iron Lad [21st century] --> Nathaniel Richards [31st century] --> Pharaoh Rama-Tut [2950 BC Egypt] --> Scarlet Centurion [modern time (divergent timeline)] --> Kang [40th century] --> Victor Timely [early 20th century] --> Kang [40th century] ----/Avengers Forever divergence/----> Pharaoh Rama-Tut [ancient Egypt] --> Immortus [master of Limbo]

True Steve, Stan & Jack clearly intended for it to be Von Doom, but with the time machine ultimately falling into the hands of Reed Richards it sort of applies either way.

According to the Official Handbook of the Marvel Universe Iron Lad takes place when Richards was about 16 years old and he didn't discover his ancestor's time machine until age 25 - putting Iron Lad before his first trip to Egypt as Rama-Tut.

edited for spelling errors

The newest edition has a timeline of his appearances which lists them by 'calendar date' starting with his time as Rama-Tut, which was pretty helpful.

I always thought they really didn't do much to explore some interesting possibilities with Kang - such as when Steve Englehart had him go back into the future to make plans only to return immediately after his defeat to attack the Avengers again (Avengers #128-Giant-Size Avengers #4 and then Avengers #141-143) and to have Kangs from multiple points in the timeline attack the Avengers together (Giant-Size Avengers #4).

Englehart of course connected Rama-Tut, Kang and Immortus, which set the whole thing into motion.  Some writers handled it pretty well (Stern, who did the great Doctor Strange/FF 'crossover' in ancient Egypt, JB and Englehart), some not so much (Busiek, who felt the need to 'fix' everything and Heinberg, who apparently didn't understand how time-travel worked in the Marvel Universe).

Kang's costume was slightly changed when he returned in Avengers #11 (the vertical lines on the front of his tunic being the obvious change), but Don Heck was pretty faithful to the model when he drew him in Avengers #23-24 (Dec '65-Jan '66).

The biggest change came when Kang returned in Avengers #69-71 (Oct-Dec '69) when Sal Buscema drew him in what has become the accepted interpretation.

The two biggest exceptions being Kirby's art in Thor #140 (May '67) and Herb Trimpe's story in Incredible Hulk #135 (Jan '71).

Another issue has been with the coloring which varied pretty wildly over the early years.  (brown?)