The Eel II: 1942, Lightning Comics v2#6 (Ace). Professor Aqua had the unique ability of being able to breathe underwater and he combined that with skills as a contortionist to make a living as part of a side-show for a circus. An accident leaves him pinned under water by a large metal pole. In desperation, he discovers that while submerged he is strong enough to snap the pole in two. He decides that he could better use these skills in crime to make a fortune than as an oddity for people to gawk at. He creates a costume for himself and embarks on his new career. He is not above murdering to get his goals and his aquatic abilities lead him being named "the Eel" which he embraces. He makes use of a shock gun to stun passengers and crews on boats as well as a weapon against the hero Lash Lightning. He is eventually captured by Lash Lightning.
The Eel III: 1942, Lightning Comics v2#6 (Ace). Strangely, this Eel appeared in the same issue. In this case, he's an inter-continental jewelry thief and smuggler. He is talented at disguise, able to pass himself off credibly as an old man. However, he's unmasked by the Raven. He does not have any apparent superpowers and is apparently not the same villain that faced Lash Lightning.
Eelo: Fantastic Comics (Fox). This fishman was a foe of Samson.
El-Buff-Ali-Rugg: 1944, Four Favorites #15 (Ace). Half Japanese-Half Moslem, El Buff creates unrest between India's fighting race - the Moslems and the rest of India, to the point of taking over leadership by killing the natural ruler and stealing the Symbol of the Eternal Kingdom which should make him invincible and the recognized ruler of the Moslems. The legitimate ruler's son and Captain Courageous defeat him.
El Conquistador: 1945, All New Comics #11 (Harvey). Dressed head to toe in armor as a Spanish Conquistador (of course, none of the conquistadors wore full plate mail armor, but why quibble), El Conquistador has taken over a tribe of ancient Mayans in Guatamala and uses their superstitions and old fear of the conquistadors to drive them to fight against Guatamalan farmers and hurt their aide of the American War effort. In addition to the tribe, they have a giant reflective disc on top of a Mayan pyramid that can be used to bring down airplanes. It is one such downed plane and missing pilot that brings Pat Parker and her Girl Commandos to investigate. They expose him as a German agent and disable his pyramid but are forced to leave him with the Mayans in order to rescue the downed pilot. The story ends with forces being gathered to go back and take care of them for good.
El Terror: 1951, Tim Holt #20 (Magazine Enterprises). El Terror is a bandit leader in the American Southwest in the late 19th Century. His reign of terror is seen by the visiting Easterner Tim Holt. Holt hears about the legends of the Red Mask from a century before and adopts the identity to put a stop to El Terror.
El Zingaro: 1941, Amazing Man Comics #22 (Centuar). A hooded and robed man who also carried a pair of revolvers, he is leading his own private army of banditos, taking over oil wells, ranches and gold mines of Mexico to fund an invasion of the US. He and his gang are stopped by the Voice who through his powers brings their headquarters down around their ears.
Electru: 1940, Thrilling Comics #4 (Better). A giant of around 7 feet tall, bald with a mustache, he had the ability to throw electrifying bolts. Not only that, but with his scientific knowhow, he had outfitted his gang with electric guns and airplanes that did the same. With these powers he attacked the Panama Canal, a Treasury building, law enforcement buildings and banks, killing all that stood in his way. Only Doc Strange (back when he was Dr. Strange) was strong enough to stand up against him. Strange didn't pull any punches either. He threw a car of the villain's henchmen into the path of a locomotive, destroyed the dynamos that powered his men's equipment, bombed the ship that served as headquarters (killing everyone on board) and punched Electru powerfully enough that he crashed into his own lab equipment and apparently killing him.
The Elemental: 1940, Amazing Man Comics #9 (Centuar). At a concert, amateur pianist Bill Wend is overcome with the desire to play and rushes the stage to do so. The music that he is compelled to play summons an alien evil being, an elemental. It grows to huge size and terrorizes the crowd, eating some of them. However, the Magician from Mars is able to match his size and brute strength and he flees. From there he enters an alliance with a "Mad Professor" who kidnaps people to feed to the elemental so it can grow in power until it can summon its brethren and conquer the Earth. The Magician from Mars is able to track them down and defeats the Elemental by singing beautiful notes, it shrinks as it loses its power agonizingly until ultimately it is sent back to the dimension from whence it came. The professor is presumably killed when the Magician from Mars brings down the staircase which he was fleeing up.
Emerald Men of Asperus: Fantastic Comics #8 (Fox). "On a certain asteroid between Mars and Jupiter dwells a manlike race of super intelligence. They are known as the "the Emerald Men of Asperus." Their leader, the High Mogul comes up with an idea to destroy the sun and then bring the Earth to their control and make mankind their slaves. However, their plans are observed by the science-wizard Stardust who uses his vast abilities to destroy their bombs and send their planetoid to some distant uninhabited system so they cannot threaten the Earth again.
Emperor: 1942, Thrilling Comics #24/25 (Better). The Emperor is a way above average Yellow Peril menace. One, he wears a type of costume. Two, in just one story he has a burrowing craft called the "Glowworm", a super gas pellet gun, a projection ray machine (that allows him to project his image and voice to deliver threats and such) AND flaming gorillas which allows him to bedevil the hero Doc Strange and attempt to take over the world. Three, he actually manages to escape capture by the hero at the end of the story. One wonders why he felt the need to team up with the rather forward thinking ace Nazi spy Kamholz (he wore a bulletproof vest which saved his life when the Emperor betrays him). NOTE: The story in issue #25 is titled "The Return of the Emperor" and is definitely written as if it's not his first adventure. However, the GCD lists that as his first appearance and doesn't list an issue #24 at all. The GCD isn't always correct though.
The Evil Eye: 1944, Dynamic Comics #12 (Dynamic Publications/Chesler). Helen Jordan has inherited a mansion haunted by a ghost called the Evil Eye. No sooner does she avail herself of the services of the detective Lucky Coyne and partner Terry, than Evil Eye makes his presence known, a shadowy figure with a frightful face. Every encounter with the Evil Eye, he manages to stay disappear and stay almost a step ahead of the detectives. However, they ultimately unmask him as Harms, the old caretaker who was after jewels that were secreted in the mansion, though the mansion itself goes up in flames (sensing a theme in the villains this go around)
Avenging Axe: 1947, Manhunt #1 (Magazine Enterprises). A diving accident lead by Olga Prentice's father killed everyone when the airlines snapped. One of the victims left a half insane brother who swore revenge on the Prentice family and became known as "the Executioner". He falls to his apparent doom when fighting Inspector Kirk of Scotland Yard.
The Eye: (Oct. 1947, Thrilling Comics 62 (Better). Called a killer and the craftiest plotter of the underworld. When Doc Strange waged a one man war on crime and gangs, this tough man with a patch over his left eye freed the caught gangsters and set out to organize a great syndicate as well as capture and kill Doc Strange. All he managed to do was ultimately join the others in jail.