Shugenja
Shugenja IRL were ascetic Monks who existed in Japan between the 7th and 14th centuries.
They were the Japanese equivalent of Shaolin warrior monks; who spent most of their days in contemplation and learning but also trained their bodies to perform spectacular feats of endurance and martial prowess.
This quest for physical perfection was what made them appear supernatural to the common man, whilst their knowledge of various topics such as philosophy and medicine gave them the legendary reputations as "wise men" and made them highly desirable advisors to diamyos, taking the equivalent roles as court "wizards" in Japanese culture.
3rd Edition D&D
Legend of the Five Rings (and by extension, Wizards of the Coast) took the supernatural approach to creating the Shugenja class, mostly driven by the pre-existing storyline of the Rokugan campaign setting, but because the closest actual analogue the Monk was already a character class and they wanted to differentiate between the two and so their amazing physical training has been mostly ignored.
It was originally printed in Oriental Adventures to fill the gap of Wizard which generally gets dropped for not being "oriental enough". It was then reprinted again in the Rokugan Campaign Setting and finally reprinted in D&D 3.5 Complete Divine.
The character class is best described as a divine mirror of the Sorcerer class in that they may cast spells spontaneously and only learn a few new spells each level, however unlike Sorcerers who just happen to know all their spells can cast them when they feel like, Shugenja have a spellbook-equivalent "Ofuda" that they must read from in order to cast their spells. Losing this item does seem like an easy way to cripple the class, but it's easier to consider it a divine focus which would have been necessity for most divine spells anyway.
There are no armour proficiencies, which would normally be horrifying for a divine caster and you only learn simple weapon proficiencies. Though in Rokugan this is explained as an essential requirement, since learning to wear weapons/armour is not socially acceptable for Shugenja, this rule just carried over to Complete Divine and you have to live with it.
Also, at character creation they have to choose both an element and a school/order, which can be simply described as a cleric's domains. Unfortunately this hobbles the class even more, as being forced to choose spells from one element then restricts you from learning any spells from its opposing element, meaning your role becomes much more focussed.
- Depending on your setting, your element also dictates which school you can join. This gives you a "domain" of spells from 1-9 that you could not otherwise get in your core list, but no additional domain ability. If you were playing within the Rokugan setting, your character's samurai clan dictates this and so you don't even get that choice.
Finally, they also get the ability to "Sense Elements" which allows them to roll to check for the presence of their chosen element within range, or it's particular substance (such as what types of mineral for "Earth"), while this sounds almost useless, a clever player can come up with neat uses such as a means of navigation or sensing the presence of hidden creatures (the water inside human bodies perhaps?)
The upside to all these restricting factors is the spell-list itself. Although they are divine casters, many of the spells on the Shugenja spell-list come from Arcane classes. Take for instance an Earth specialised Shugenja: his primary abilities are buffs from the earth element but since he has not restricted himself from the Fire element he can fling around fireballs and do some actual damage, and since he has also not restricted himself from the Water element he can heal his allies too.
This utility within the list itself gives the Shugenja the ability to fill the role of different casters within the group and is actually ideal for very small groups where he might be the only caster OR as a backup utility caster where other casters might be more specialised.