Henry Mortonson was cursed with a birth defect that not only forced him to perpetually smile, but also gave him an appearance that resembled a hyena, which he soon adopted as his name.
Following the outbreak of World War II, the American born Mortonson became a supporter of the Nazis aiding in acts of sabotage in the United States on military vehicles. In 1942 he and the Shark were selected by Agent Axis on a mission to attack member of the Invaders. He was given the task of capturing the original Human Torch and take a sample of his synthetic blood. The Hyena succeeded in capturing the Torch and extracting the blood, but before he could kill the hero, the Torch was pulled out of time by the cosmic entity known as the Grandmaster. Later, the Torch and his allies returned and captured Hyena and his allies.
By 1948, the Hyena had somehow avoided War Crimes trials and with the fall of the Nazis took his skills of sabotage to the highest bidder. He was hired by Mr. Lennox to sabotage the trucks owned by the Miller Trucking Company in order to force it's owner Lorraine Miller to sell the company. However, the Human Torch and his partner Toro began investigating the truck crashes and eventually captured the Hyena and Lennox.
Sent to prison, the Hyena vowed never to smile again and through force of will managed to do so. While in prison over the years he invested in experts to study the Human Torch and learned of his android nature, hoping to someday get revenge. He learned that the Torch's ability to flame on would eventually fade away after his body naturally reversed the original design flaw of his creators design. It was not until the modern age that the Hyena was released from prison. Learning that he had a terminal case of cancer and not much to live he moved into Gingerbread House in Los Angeles and began plotting his revenge against the Human Torch. About that time, the Torch (recently revived after years of inactivity) had lost his ability to flame on. Learning this Hyena developed a device that would not only restore the Human Torch's powers but also detonate a massive amount of explosives he had planted in the Los Angeles area. He then sent the word to the Torch that he knew the location where the body of his sidekick Toro was buried. Answering the call, the Torch was instead attacked by the Hyena's men and found a note from the Hyena on one of his men offering to restore his powers.
The Torch came to the Hyena and listened to his proposal, point out the device would link him to the worlds computers and jump start his powers, and that he would exchange this renewal of powers in exchange for information the Torch gleaned from law enforcement databases. The Torch agreed and wire himself into the machine. The machine then caused numerous disasters in the Los Angeles area which were quelled by the Torch's team mates in the Avengers West Coast dealt with the crisis until Henry Pym deactivated the signal from the device. Having resisted the urge to flame on and activate the explosives, the Torch pulled the device away from the Hyena and smashed it. The Avengers West Coast then stormed his home and subdued his minions. The Hyena explained his motivations and terminal illness before seemingly keeling over dead from his illness. However, the Hyena survived and woke up in hospital to be informed that due to his unique physiology his cancer was affected by his personal happiness. Since he was happy the past couple days plotting his revenge against the Torch the illness went into complete remission. The Hyena was horrified that he now had many more years to live once more in prison and demanded the Torch and his comrades to leave.
It appears that due to his unique physiology caused the Hyena to age slowly allowing him to live on well into the modern era. His longevity and healing ability also appears to be effected by his happiness as when he was diagnosed with terminal cancer a change in his mood allowed him to fight off the illness.
The Hyena's unique physiology had caused him health problems later on in his life. He contracted a rare and terminal form of cancer which was effected by his personal happiness. When he was bitter an miserable the cancer ravaged his body. This cancer went into remission when he was happy. It is unknown if another extended period of misery would cause the cancer to return.
During the 1940s the Hyena was an expert saboteur, he access to various fire arms and explosives. In the modern age he developed a device that could trigger explosives and cause various mechanical failures when the device was wired into the Human Torch.
In Avengers: West Coast #83 the Human Torch recounts his various encounters with the Hyena. He states he met the Hyena for the second time during 1947. The issues footnotes state that this encounter was in Human Torch Comics #27 which was published in 1947. This is incorrect as the Hyena first appeared in Human Torch Comics #30, published in 1948. It can be factored that both the footnote and the year referenced are incorrect.