The Mark IV Armor was Tony Stark's fourth Iron Man suit and was built to replace the Mark III after it was heavily damaged in Stark's fight with Obadiah Stane. Because it was built to be a direct replacement, the Mark IV is very similar to the Mark III with only a few minor changes.
After the Mark III suffered irreparable damage in Stark's battle with Obadiah Stane's Iron Monger Armor, Stark built the Mark IV suit to replace it, becoming the primary suit that Stark used in all of his activities as Iron Man. During the Stark Expo, Stark air-dropped to the main presentation stage in the Mark IV suit to make a grand entrance and give the opening speech, sporting a tuxedo underneath the armor.
Made to serve as a direct replacement for the damaged Mark III armor, the Mark IV carries over many of the same capabilities and functions, while only making a handful of advancements.
The Mark IV enhanced the user's physical capabilities, granting them superhuman strength, near bullet-proof durability, and enhanced movement, speed and reflexes. The suit also carried over the repulsor technology, allowing for sustained flight while also serving as the suit's main weapon along with a greatly improved uni-beam.
The Mark IV also carried over the other weapons systems present in the former suit, including: multi-fire, computer targeted mini-guns in each shoulder, high explosive, anti-tank missiles housed in each forearm, and non-weaponized flares contained in two circular launchers located at the suit's hips.
However, even while retaining most of the previous specifications, Stark was able to improve various details of the suit's visible design such as the suit's internal mechanics as well as the design of the metal plating for the arms, legs, and chest to allow for a better fit and more mobility while wearing the armor. This possibly also made it easier to put the suit on and take it off.