Most video game RPGs, from their beginning, have included some kind of attack management. In early menu-based combat games, like Wizardry, it was simple. You had six characters in a party, and the first three could be hit by melee attacks, while the back three could only be hit by missiles and spells. So naturally, you wanted heavily armored characters with a lot of health (known as "tanks") in the front, while "squishy," easily-killed characters in robes should have been placed in the back. Within those constraints, enemies seemed to attack randomly. Hybrid real-time/turn-based games like Dungeon Master and Eye Of The Beholder used similar systems, but with the possibility of being attacked from the side or rear.
RPGs with tactical combat, like the middle Ultima games and the Gold Box series, were only slightly more complicated. You still wanted your heavily-armored fighters in the front lines, and the game engines had rules that made enemies not simply run by them. For example, in the AD&D rules of the Gold Box games, if an enemy is adjacent to a character and then moves away from them, that character gets a free opportunity attack. The AI, moreover, seemed to be programmed to avoid that, even when it probably would have been to its advantage to take the hit and attack the mage.
Two things complicated these perhaps too-simple systems: the rise of real-time combat, and practical multiplayer and massively multiplayer RPGs. Real-time games like Baldur's Gate introduced a level of chaos largely impossible in turn-based games. While the real-time games did allow some micromanagement to attempt to control the chaos, it was still largely unpredictable: press button, hope your tiny people beat all the enemy tiny people without dying.
Multiplayer games offered a conceptual shift as well. In a single-player game, even one with a party, an enemy attacking one of your characters was still attacking a projection of "you" within the game. The challenge is dealing with that. Online, that's different. Your character is one of many in a grouping, and if you're not being attacked, you have no challenge. Moreover, almost every online RPG has been real-time, and would suffer from the same issues as single-player real-time games in terms of chaotic enemy attacks.
So new systems were devised, although they were rarely transparent to players. In Ultima Online, the character who seemed to be doing the most damage got "aggro," or targeted by enemies. Given its free-form skill system, where you could be a powerful mage and wear the best armor, this wasn't a huge issue. By the advent of Everquest, however, with its much more specific and rigid class system, concepts of tanking solidified (it's possible that other games used similar forms to Everquest, but EQ certainly popularized them) . It makes sense: classes have to balance amount of damage and survivability. Heavily-armored warriors who can also deal massive damage will have an inherent superiority to mages or rogues. So tanking warriors do less damages. But then having enemies attack whoever's doing the most damage, or randomly, the tanks never have a chance. This requires a mechanic to control aggro: threat.
"Threat" is built up by actions outside of simply damaging an enemy. Healing generates threat, attacking generates threat, and most importantly, tank classes have skills that generate threat. "Taunt" skills that force an enemy to attack a tank are the most common, and even existed outside multiplayer games. By the time of Everquest, you had different ways to manipulate threat: "Pacify" skills for healers to lower threat, and various other skills for warriors to generate it without doing damage: for example, "Sunder" was the preferred choice early in World Of Warcraft. A character no longer simply was a tank by virtue of hit points and armor, but had to engage in the act of "tanking," or using the proper skills to generate threat and maintain aggro.
As with so many things, what Everquest began, World Of Warcraft solidified. Early boss fights and raids were often straightforward "tank-and-spanks," where one character held aggro while being healed, and others attacked the boss freely (doing as much damage per second as they could, or "DPSing"). But clever modders soon began to test ways to measure the previously opaque threat mechanic. Add-ons like KTM (the KLH Threat Meter) made it numerically clear. Now players didn't have to guess whether they'd draw aggro, but instead just had to watch a meter. I remember reading interviews with developers who said that the threat mods forced them to completely rethink their boss fights: threat's importance was even surprising game makes.
But then an funny thing happened: threat, along with a few other MMORPG mechanics, started seeping back into single-player role-playing games. Japanese RPGs have led the way on this, perhaps surprisingly, starting with Final Fantasy XII. But in 2009, the highest-profile traditional western RPG, Dragon Age: Origins, started explicitly using a threat system. Warriors and shapeshifting mages had skills specifically designed to build threat and draw aggro (a system continued in Dragon Age 2).
Even games that don't specifically use threat systems still include tank mechanics in a way that simply wasn't done 15 years ago. Hirelings and companions in the new Fallouts and Skyrim function in this fashion: Skyrim's Lydia is an effective tank if you're a ranged fighter/magic-user, while bow users like Aela did better if you were a hand-to-hand fighter. Paying attention to threat and aggro, and learning how to tank, has slowly become a crucial component of the role-playing genre.