1996—AD&D 2e, but it wasn’t a separate class
As another answer of mine discusses, the 1996 Player’s Option: Spells & Magic for AD&D 2e introduced “artificer” as a “kit” (kind of like 5e’s subclasses) for the wizard class. The artificer focused on item-improving magic, so that much is similar to the Eberron artificer, but since Eberron itself didn’t exist yet, the 2e artificer was necessarily very different from the one we know today.
The 2e artificer’s big thing was the ability to store spells in items. This meant that they could have vastly more spells available at a time than a regular wizard, but it took a week of solid work to store a single spell in this manner. A potentially-significant benefit of this ability is that stored spells could be released “with a casting time of 1” regardless of the spell’s usual casting time. I’m not super-conversant in 2e, but it seems likely to me that it might be useful to store spells with long casting times so they could be released more quickly than they could ordinarily be cast.
2004—D&D 3.5e, first publication of Eberron, including its iconic artificer
Eberron Campaign Setting was a sourcebook published for D&D 3.5e detailing, shockingly enough, the Eberron campaign setting, which was brand-new at the time. It introduced a new artificer character class to 3.5e, which didn’t have “kits” or anything like them, and hadn’t replicated the artificer option for the wizard class.
The new artificer wasn’t a wizard, and technically didn’t cast spells at all—instead, it cast “infusions,” which are literally identical in every way to spells but technically aren’t. The main things about infusions is that they were neither arcane nor divine (as every true “spell” in 3.5e was) and they could only target items, objects, and/or constructs (though that wasn’t unique; plenty of existing spells shared that property). Its other class features were dedicated to creating and using magic items, including magical construct minions.
The Eberron artificer did replicate the spell storing option of the 2e artificer, though it was perhaps less unique—any spellcaster in 3.5e could easily create scrolls and wands for that purpose. But the artificer was simply better at it than other spellcasters, and on top of that had an infusion for creating a temporary “wand” on short notice.
2009—D&D 4e Eberron update including the artificer
2009’s Eberron Player’s Guide brought Eberron into D&D 4e, including the artificer class. Within 4e, the artificer was a “Leader” class, meaning it focused on buffs and healing. Its special trick was that its healing could be handed out to other characters ahead of time, which could trigger them on their own without the artificer’s involvement. This is again perhaps reminiscent of the 2e specialty of storing spells.
Aside from that, the 4e artificer was explicitly an arcane class, and therefore cast spells—no non-arcane, non-divine “infusions” here (though its healing ability was “Healing Infusion”). It also retained some ability with magic items—being able to restore their daily powers or empower them—and also knew some magic-item-creating rituals by default.
2019—D&D 5e Eberron update including the artificer
A decade later, Eberron: Rising from the Last War brings Eberron and the artificer to D&D 5e. A similar repertoire of item-improving spells as previous artificers are on display, and “infusions” are now special artificer-only features that allow them to create specific magic items, including some unique ones that aren’t otherwise available. The 5e artificer is in a somewhat awkward place as there aren’t any core 5e rules for creating magic items, but the infusion system is a pretty solid approach to handling it.
Note that, prior to Eberron: Rising from the Last War, numerous “artificers” were tested for 5e as Unearthed Arcana content. We have a question about that history, if you desire details.