Both Loki from Thor and the Red Skull from Captain America: The First Avenger are popular villains from the Marvel comic book universe. By the end of their respective films, their fates are both very much up in the air. They both disappear in ways that imply they might be dead, but definitely leave the door open for their return. This is largely where the similarities between the two characters end.
Both Loki and the Red Skull have superhuman powers, but they came about them in very different ways. Loki was born into a family of gods who have magical powers and it is later revealed that he is not the son of Odin, who is King of Asgard. Instead, he was actually born a Frost Giant, the mythical enemy of all Asgardians. Despite his pedigree, Loki is still a capable magician who can use his skills to give those powers to other people, among many dangerous skills
In contrast, the Red Skull was merely born a human, Johann Schmidt. He grew up human on planet earth his entire life. His superhuman powers were given to him much later in life, as a middle-aged adult. He was a high-ranking officer in Hitler’s army during World War II. The Nazis injected him with a serum that was supposed to make him almost immortal and unbeatable. He would still be human, but with the strength, endurance and metabolism of a superhuman.
Unfortunately for Schmidt, the experiment went awry and though he did get some superhuman powers from the serum, he was also permanently disfigured. He became red skin and bones, hence the name Red Skull. He becomes the arch-nemesis of Captain America because “Cap” as he is often called has made it his mission to defeat the Nazis, particularly HYDRA, which is run by the Red Skull. Cap got a similar dosage of serum, but it worked properly on him unlike Schmidt, who turned evil incarnate and looks like it too.
The Red Skull is loved by nobody. Even his minions and right-hand men are there out of fear. He has no love in his heart either, which makes him the perfect ruthless villain. Loki, on the other hand, is loved by his adoptive parents and brother Thor. Although the anger and resentment he feels upon learning of his adoption sends him into villainy, he was not always that way. Throughout his evil turn in Thor, the audience can sense his conflict. Part of him wants to let the anger wash over him and turn him truly evil. The rest of him wants to go back to the way things once were.
Schmidt as the Red Skull has no such confliction. He does not dwell on his fate or how fair or unfair life is. He just continues on his mission for power ruthlessly and without a second thought. It does not matter who he has to step over or even kill to get what he wants. This cold, calculating manner is completely different from Loki, who has a plan but seems almost fearful of any regret he may have upon enacting it.
Despite the huge contrasts in how they achieved and used their powers, both Loki and the Red Skull are highly entertaining villains with back stories that are very interesting. This proves that there does not have to be similar or stock mythology used to make the bad guy intriguing in a film. These characters show that even the most disparate of backgrounds can still be fodder for evil, villainy and fantastic showdowns with their arch-nemesis that are the basis for so much of the Marvel comic books and movies.