And now for something completely different.
A common method for teaching Dungeons & Dragons mechanics is to place them in cultural context. This is especially true for teaching races and classes. Human fighters are self-explanatory, but it's not obvious if elves are the Santa's workshop sort or the JRPG sort. Rogues can sound like an evil profile, but remember Robin Hood who gave to the poor.
I personally believe that the druid class can be particularly challenging to teach. There are few druids in pop culture. I've mostly seen new players advised to think about 'the brown wizard in the Hobbit movies' (read: Radagast) for circumlocution. Many people come away thinking that druids are the ugly duckling of magic users. Others come away fixating on the 'animal' thing, with no respect to the intended philosophy of druids.
I have a novel proposal: Salazar Slytherin from the Harry Potter universe is a prototypical druid.
One of core traits of the druid class, and indeed the trait that attracts the most interest from new players, is their connection to animals. Druids can use magic to speak with animals and shapeshift into animal forms. They partner with an animal familiar. Personality-wise, they are pet parents.
Salazar was obviously a snake person. They are the mascot and motif of his Hogwarts house.
His most well-known ability was Parseltongue, to the point that the Gaunts (up to and including Tom Riddle) only had to demonstrate that ability to make a claim on Slytherin's legacy. This is the clearest link to druidity for Salazar. And the ability to talk with animals is rather frequently the entire reason players pick that class. Salazar will effectively communicate these details, whereas Radagast's best parallel is having a rabbit-drawn sled.
Salazar's basilisk is also one of the most prominent familiars in the Harry Potter universe. I'd argue the only competition is Hedwig and Fawkes. The basilisk and the chamber that Salazar built for it are the titular topics of an entire book, after all.
And what a familiar it is! Basilisks have a range of abilities that are both role-play and combat oriented, while also being balanced by lore-derived weaknesses (i.e. roosters' crowing). This could go a long way to preparing new players for the choice of a familiar.
Needless to say, the fact that Salazar made that labyrinth inside the school further emphasizes his care for the animal. There can be little doubt that he was a bit obsessed. While it can be unfortunate (as alluded to above), this is what many new players fixate on for thinking about druid. But surely Salazar's template could not make the misunderstanding worse.
Druids are also deeply connected to nature. In D&D, this largely means elemental magics (as opposed to god-derived magics; or unnatural, evil magics). The Harry Potter universe does not divide magic into elemental disciplines, instead preferring categories like Transfiguration and Divination.
Let's leave aside the Dark Arts.
Let's instead consider Hogwarts for what it is. A stone castle of traditional construction. Located in Middle Of Nowhere, Scotland with just a small commercial town nearby. Beset by by merpeople-inhabited lakes and forbidden forests. Isolated not just from the trappings of modern urbanism, but also from the (unnatural?) distractions of government and press and the consumer economy. Salazar and the co-founders certainly seem to have a disposition towards nature.
Druids are also devoted to a philosophy of balance that is colored by their worldview. Again, in D&D, this largely has to do with nature as elemental magics. They are motivated to action in defense of this balance.
Salazar certainly had opinions about the balance of magical society. Unfortunately, his worldview was colored by racism and bigotry. He and his basilisk were happy to 'defend' that balance, too.
This is a stretch, I know, but perhaps could demonstrate how an evil-aligned druid could be written?
In summary, while Radagast is an option for relaying the concept of druids in Dungeons and Dragons, I believe Salazar Slytherin is the superior choice.