Howard Stark was a brilliant inventor and businessman and the father of Tony Stark/Iron Man. He founded Stark Industries. And during WWII he worked on various government projects, including the Manhattan Project and "Project: Rebirth". Howard also helped the Strategic Scientific Reserve fight against HYDRA.
World War II
Howard Stark was an eccentric industrial genius, inventor, and businessman. He founded Stark Industries, was the top engineer for the the Strategic Scientific Reserve. Stark proudly showed off multiple world-changing inventions at his World Exposition of Tomorrow in 1942, including a flying car and a prototype android. Secretly, however, Stark was working with the allies in order to help in World War II, performing multiple experiments for them and working as their weapons specialist.
During the second World War, Howard was instrumental for "Project Rebirth", the project of the SSR that Steve Rogers underwent in order to become U.S. Army's first Super Soldier. Howard built a machine that used up half of the power in Brooklyn to dowse Rogers with vita-rays after receiving the super-soldier serum developed by Dr. Abraham Erskine. The process successfully transformed weak and scrawny Steve Rogers into the muscular Captain America, though Dr Erskine was soon assassinated by a HYDRA agent.
When Cap was going on a solo mission to save his friend Bucky and the POWs that were captured at a HYDRA base, Stark personally flew him where he needed to go, and afterwards constructed his shield from pure vibranium and also made for Steve an upgraded military uniform to use as Captain America. When Captain America crashed in the ocean with the Red Skull and the Cosmic Cube, Howard refused to abandon his friend, and charted multiple expeditions out the ocean to search the sea for him. Though they failed in their search, they did discover the Cosmic Cube, laying on floor of the ocean after falling out of the Red Skull's craft during the crash. He attempted to figure out how the Cosmic Cube worked, but had less than helpful results.
Post War
After WWII, he shared Stark Industries with close friend Obadiah Stane, and together they were responsible for the development of many weapons for the U.S. military. Along with government associates, Howard has become a founding member of S.H.I.E.L.D. In 1954, Howard created the Stark Expo, a world wide technology fair where the world's new technology would be presented to show a bright future for mankind.
He also co-developed the arc reactor with defected Soviet scientist Anton Vanko. Though the power of the arc reactor was immense, Howard saw it as the stepping stone to create a new, stable element that would render nuclear power obsolete. However, Anton saw the arc reactor as a way to get rich and when Howard found out, he had Anton deported back to Siberia.
At that time, he met a woman called Maria with whom they had a son, Tony. Howard never showed his son any love, which Tony despised him for. However, deep down, he cared about his son, and had high hopes that Tony would someday change the world. Howard was limited by the technology of his time and could not finish the new element, so he embedded the atomic structure of the new element in the 1974 Stark Expo model, and a message to Tony in one of his old home movies, stating that he had high hopes that Tony could figure it out with the current technology and change the world. Before the film ends, Howard said that Tony was and always would be his greatest creation.
Death and Legacy
Howard and Maria were killed in a car accident on Long Island in December 1991, and their son inherited Stark Industries, becoming the youngest CEO of a Fortune 500 company, at age 21. After watching the 1974 message video and examining the Expo model, Tony discovered the new element, noting that his father was still teaching him even after being dead for over two decades. The new element was the key to a safer and more powerful arc reactor, which Tony needed to power the electromagnet protecting his heart without poisoning his blood, like what the palladium had been doing to him. Creating a miniature accelerator in his basement lab, Tony was able to synthesize the new element, upgrade the design of the arc reactor to clean his blood, and create the powerful new Mark VI armor.
The Avengers
Howard Stark's file is among the ones Rogers studies after his awakening in the present days, and he's obviously reported as "Deceased". Howard's past association with Captain America is referenced when Tony notes that his father talked about Cap a great deal, although Tony initially expresses doubt towards Rogers' abilities until he sees the super soldier in action.