When Spider-Man met a similarly-powered man named Ezekiel, Ezekiel explained to him that Spider-Man's powers were not an accident, and that the spider that had bit him did so voluntarily to pass its abilities onto Peter before it died. This made Spider-Man a "totem," a bridge between man and beast, with the properties of both. Ezekiel then warned Spider-Man that, as a totem, he was in danger from those who would seek to destroy such beings. One of those, who showed up soon after, was Morlun.
Little is known about exactly what Morlun is and where he comes from. According to Ezekiel, as long as totemistic forces have walked the earth, there have also been those who have fed on them. While Morlun and his brothers (it is not known how many there are in existence, but Morlun is not the only one) can subsist on the life forces of normal humans and non-totemistic superhumans for a time, they always crave a pure host and Peter fits the bill perfectly.
After Peter's meeting with Ezekiel, Morlun and his hapless minion Dex subtly began tormenting Peter from the shadows, stalking him and wreaking havoc with his spider-sense. Morlun finally revealed himself when Spider-Man was investigating a fire at the wharfs, punching him with what Spider-Man claimed was the hardest punch he had ever felt. Morlun then told Spider-Man that he would eventually kill him, and now that they had made physical contact, he could find Spider-Man wherever he went. Though Spider-Man fought back, Morlun continually regained the upper hand. Peter tried to flee, but Morlun was able to find him easily and resume the fight. Spider-Man finally got away after Morlun burned down the building they were fighting in, but Ezekiel told him it was no use. Morlun would find him once again, and kill him.
Morlun continually attacked Spider-Man over the next few days, endangering the lives of innocent citizens if Peter tried to flee. With Ezekiel's help, Peter managed to briefly escape with a sample of Morlun's blood, which he discovered contained the DNA of every genus in the animal kingdom. Realizing that Morlun's DNA was pure, Peter found a weakness he could exploit. Luring Morlun to a nuclear power plant, Spider-Man injected himself with a dose of radiation that would kill a normal human being, but was only enough to weaken him due to the radiation already in his blood. When Morlun arrived, he prepared to feed, only to be burned instead by the radiation in Peter's blood. Peter explained that he wasn't a pure spider totem as Morlun had guessed due to the spider that bit him having been previously subjected to a dose of radiation, and that while Morlun could feed on the spider, he couldn't digest the radiation. Absorbing the radiation rather than his spider-powers with every punch Peter threw at him, Morlun began to disintegrate, and he pleaded for Spider-Man to spare his life, saying he was merely doing what was necessary for his survival, and that it was nothing personal. While Peter debated on whether or not to let a monster like Morlun go, Dex suddenly appeared and shot Morlun, causing him to crumble to dust.
Morlun mysteriously returned months later and plagued Spider-Man by sudden and mysterious appearances, warning him that he was coming to finish him. Spider-Man, for a reason not explainable by science, was dying, and Morlun hung back to watch the causes and effects of his ailment. Finally, Morlun struck, and in a climactic battle, brutally beat Spider-Man. Morlun left when the police arrived, opting for a more appropriate time to absorb Spider-Man's life force, leaving the web slinger one-eyed and near-death.
Returning soon thereafter, Morlun entered Spider-Man's room in the Emergency Ward and prepared to feast, apparently unconcerned about the presence of the Avengers (of the New Avengers line-up) in the hospital to check up on their teammate - Captain America, Iron Man and Luke Cage had come in the front door while Mary Jane and an uncostumed Jessica Drew sneaked in around the back. Mary Jane, who arrived at Peter's room just as Morlun was about to feed, tried to stop him, but he casually broke her forearm and threw her off to one side. As it appeared he would kill her, Spider-Man suddenly sprung to life in a ferocious display of mysterious new powers, including stingers sprouting from his arms that he used to pin Morlun down, and fangs that he used to rip Morlun's throat out. Morlun apparently died once again, crumbling to dust, weakly saying that it wasn't supposed to be this way.
Sometime later, a secret group resurrected Morlun so that he could devour the Black Panther and in turn weaken the nation of Wakanda. As a start, Morlun slays the long-term Panther adversary Man-Ape. He was defeated by the new Black Panther Shuri, who, with the help of a witch-doctor, sent Morlun into limbo, where he was forced to battle the endless hordes of Death.
Morlun later appeared alive, as he travelled to Earth-311, and killed and drained the life essence of that universe's Spider-Man, Peter Parquagh.
Morlun possesses a variety of superhuman attributes as a result of his unique physiology.
Life Force Absorption: Morlun's primary power is the ability to absorb the life force energy of other living creatures, thereby granting himself superhuman physical abilities. Even though Morlun can absorb the energies of virtually any being, he must occasionally renew himself by feeding upon pure forms of animal-related superbeings from one of the four categories that make up his own, unusually pure, DNA such as animal, insect, human, and bird. Once Morlun has touched a human, he is able to sense that person's life force across great distances. While the limit of this ability isn't known, it allowed him to easily follow and track Spider-Man across New York City.
Superhuman Strength: Morlun possesses superhuman strength that varies according to how recently he has fed and on what kind of source, but he has demonstrated strength capable of lifting an estimated 20 tons. While fighting the Black Panther, he ripped apart an adamantium net with his bare hands. Spider-Man states that Morlun's punches are the hardest he has ever felt.
Superhuman Speed: Morlun can run and move at speeds that are beyond the physical limits of the finest human athlete. Though the exact limit is unknown, he has been shown to climb several flights of stairs and cover several blocks in only slightly more time than it takes Spider-Man to reach the same destination by web-swinging.
Superhuman Stamina: Morlun's musculature produces less fatigue toxins than the fatigue toxins of human beings. While his stamina depends upon he's fed, Morlun can physically exert himself at peak capacity for at least several hours before the build up of fatigue toxins in his blood begins to impair him.
Superhuman Durability: Morlun's body is tougher and more resistant to certain types of injury than the body of a human being. It is known that Morlun can withstand great impact forces, such as being physically struck by Spider-Man, that would severely injure or kill a human, most notably being hit by a vibranium-tipped nuclear missile. The limits of his body's resistance isn't known. For example, it is unknown if he is resistant to penetration wounds from bullets or bladed weaponry.
Superhuman Agility: Morlun's agility, balance, and bodily coordination are enhanced to levels that are beyond the natural physical limits of the finest human athlete.
Superhuman Reflexes: Morlun's reflexes are similarly enhanced and are superior to those of the finest human athlete.
Immortality: Morlun is functionally immortal in the sense that he is immune to the effects of aging and all known diseases. However, he can be killed if wounded severely enough.
Even though it isn't known exactly how much, if any, formal training he's had, Morlun has proven himself to be a formidable hand to hand combatant.
Morlun must regularly feed on the life forces of other living beings to stay alive. However, in order to renew himself and to prolong his extremely long lifespan, he must feed on totemic (purer) sources occasionally. Morlun has also proven highly vulnerable to exposure to high levels of radiation. However, Morlun must always be concentrating on keeping himself invincible. He eventually lets his guard down when he is feeding. This weakness enabled Ezekial to break his nose and Spider-man to kill him. When his guard is down, he is as vulnerable as any regular human.