Doctor Strange has been around almost since the beginning of Marvel Comics. When Marvel started producing superhero comics, the company acquired titles including Strange Tales. With issue #101, Marvel began introducing superheroes to the book and Doctor Strange arrived in issue #110 for the first time. That title changed its name to Doctor Strange with the 169th issue and introduced fans to mystic characters from all realms of the universe.
In both the Strange Tales series, and later the different versions of Doctor Strange comics, Stephen Strange befriended some iconic allies, traveled to other dimensions to meet some legendary characters, and developed his own interesting rogues' gallery. While most of the characters introduced in Doctor Strange comics were based on magic and mysticism, some moved on to bigger and better things over time.
Wong (Strange Tales Vol 1 #110)
In the very first appearance of Doctor Strange in Marvel Comics, his loyal and longest-lasting ally also made his first appearance. This was Wong, who, at the time, was Strange's version of Alfred from Batman comics. While he wasn't given a name in his first appearance, he has survived the test of time.
Wong's original origin had him as one in a long line of his family to serve the Ancient One, the Sorcerer Supreme of Earth. When Strange took over the role, Wong moved on to serve him. Wong recently finally left Strange after a disagreement in the comics, and Wong plays an essential part in the MCU, as he has been the Sorcerer Supreme since the blip.
Nightmare (Strange Tales Vol 1 #110)
The first villain that Doctor Strange fought in his comics was a mystical villain that has also stood the test of time. This was Nightmare. In his first adventure as the Master of Black Magic, Strange set out to help a man tormented by nightmares and learned the villain was Nightmare, one of his ancient enemies.
In Marvel Comics, Nightmare rules the Nightmare Realm in the Dream Dimension and is widely considered one of the most powerful magical beings in the Splinter Realms. Nightmare became one of Strange's most persistent villains, but also fought other heroes over the years, including Spider-Man, Black Panther, Moon Knight, and more. He is rumored to be the villain in the upcoming videogame Marvel's Midnight Suns.
Baron Mordo (Strange Tales Vol 1 #111)
Baron Mordo has been the main enemy of Doctor Strange for most of his existence, and he, in fact, made his debut in Doctor Strange's second comic book issue, Strange Tales #111. In this issue, it was shown that Doctor Strange had taught Mordo years before and the Baron was now back to take his place as the Earth's most powerful magician.
Mordo remains considered one of Strange's most important villains, appearing in both of his MCU movies to date. Mordo has been a key antagonist and at times a reluctant ally of Strange, showing how powerful he is as a magic-user in the world of Doctor Strange.
Clea (Strange Tales Vol 1 #126)
In Strange Tales#126, Doctor Strange met his most powerful villain and his most beloved ally. The ally was Clea, the daughter of the demonic Dormammu. In this issue, The Ancient One sends Strange to the Dark Dimension to stop Dormammu from crossing over and it is there he meets Clea.
He was unaware of Clea's relationship with Dormammu at the time, but soon she chose to travel with Strange and leave her world behind. Clea ended up leaving Doctor Strange comics for a long time when he erased his existence from her memory, but she recently came back and is the new Sorcerer Supreme in Marvel Comics, showing her immense importance in the universe.
Dormammu (Strange Tales Vol 1 #126)
Doctor Strange had never faced anyone as powerful as Dormammu before he set out to fight him in Strange Tales #126. Dormammu is the Lord of the Dark Dimension, and he has always had dreams of crossing over and conquering the universe as well. It has always been Strange's job to stop him.
That was the main plot of the first Doctor Strange movie as well, as Dormammu has always used other characters to make his move. Throughout Marvel Comics history, there has never been an antagonist as dangerous as Dormammu for Dr. Stephen Strange.
Eternity (Strange Tales Vol 1 #138)
There have been a lot of hints at the elder cosmic beings in Marvel Comics. Whether it is in Eternals or as seen in the trailers for Thor: Love and Thunder, it seems that Eternite, The Living Tribunal, and more could be making their way to the MCU. They originally appeared in Doctor Strange comics, with Eternity showing up first.
In his first appearance, his power was shown when Doctor Strange asked for his help in beating Dormammu and Eternity told Strange he was strong enough to win on his own. The only being more powerful than Eternity is The Living Tribunal, but he only shows up when there is a threat to the entire universe.
Living Tribunal (Strange Tales Vol 1 #157)
It only took 19 issues after Eternity showed up for the first time before The Living Tribunal made his first appearance in Marvel Comics. This was in Strange Tales #157 where The Ancient One passes on his powers to Strange and the Doctor uses black magic to defeat his enemy.
This brought The Living Tribunal to Earth. As the all-seeing judge, jury, and executioner of the universe, he determined at the time that Earth must be destroyed. This plays into the character's appearances since that time, as it is his job to keep all of the universe aligned. His biggest role came years later with the Infinity Gauntlet storylines. He even showed up as an Easter egg in Doctor Strange and the Multiverse of Madness.
Doctor Voodoo (Strange Tales Vol 1 #169)
Doctor Voodoo, at one time, took Doctor Strange's place as the Sorcerer Supreme on Earth. While Doctor Strange was not in the issue when Voodoo first appeared, his debut came in Strange Tales #169 when he was the featured character with his introduction.
While this was not technically a Doctor Strange issue, the use of Strange Tales ensured that Voodoo and Strange would be linked from this point on. Voodoo bounced around the Marvel Comics Universe in supernatural comics before the Eye of Agamotto revealed that Voodoo was the best candidate to replace Doctor Strange as the Master of the Mystic Arts on Earth.
Zelma Stanton (Doctor Strange Vol 4 #1)
There have not been many new characters who debuted in Doctor Strange comics that made a real difference. One of the more interesting ones appeared in Doctor Strange Vol. 4 #1 with Zelma Stanton. When she first appeared, she was a librarian who was infected with Mind Maggots.
After he cured her, Strange offered her a job as his librarian and she accepted. Zelma ended up saving Strange's life, but by sacrificing her own. When he saved her, it opened up the world of magic to her and she became his apprentice and one of his closest companions ever since.
Bats (Doctor Strange Vol 1 #381)
Bats is one of the most popular characters introduced in Doctor Strange comics in many years. Originally, Bats was a basset hound left in a shelter who finally came under the care of Doctor Strange, who was working as a veterinarian at the time. Strange then used his magic to allow Bats to talk to humans and understand what they said back to him.
Sadly, Bats tried to help Strange when he was battling Loki, but he died of a heart attack. When Strange needed to use the Yggdrasill tree to get his power back, he offered it Bats' corpse. As a form of apology for his death, Loki eventually found a way to bring back Bats as a ghost dog. He has since become a fun side character, especially by becoming friends with heroes like Spider-Man.