Mr Still-water 水镜先生 (shǔi jìng xiān shēng)
[Note: “Still-water" is a metaphor of sorts commonly used to describe an unattainable level of wisdom and calm.]
Who is he:
An odd recluse that, despite having very little airtime in the story, is one of the most pivotal person that changed the course of history (at least in the fictional account). Si Ma Hui was the person responsible for nurturing the two greatest minds of that era, Pang Tong 庞统 and Zhu Ge Liang 诸葛亮. It is also he that introduced Zhu Ge Liang to Liu Bei 刘备 when the latter stumbled across his villa. There is also a related legend that says Si Ma Hui nurtured a total of 7 geniuses, which includes Pang Tong and Zhu Ge Liang as well as Guo Jia 郭嘉 and Si Ma Yi 司马懿.
Character ability 1: "Enlighten 授业 (shòu yè)"
In the action phase, you can discard one on-hand card and let any player (including yourself) draw 2 cards from the deck. Limited to one use per turn.
Character ability 2: "Dispel 解惑 (jiě huò)" [Single-use ability]
In the action phase, you can discard 4 cards, each of a different suit, and allow 1 player that died between your previous turn till this turn to revive. The revived character will have 3 units of health and can immediately draw 3 cards from the deck.
Ability's relation to story:
The ability "Enlighten" does make some sense. He is known as the teacher of the very best minds of that era, and gaining knowledge does equate to gaining power (cards)... i think. Well, that definitely makes more sense than being able to revive someone from the grave!!! "Dispel" is just completely ridiculous and overpowered! No, i do not think the teacher of geniuses can resurrect the dead.
Side note here: "Dispel" may not work as easily as it sounds. Since Si Ma Hui can only hold 3 cards max at the end of the turn and he has one "draw2" by default, the chances are low that he would have a complete 4-suit set when it is needed.
Additional info based on story:
It is said in folklore that 7 geniuses were under the tutelage of Si Ma Hui, but the stories differ greatly. One version claims that Zhu Ge Liang, Pang Tong, and Xu Shu 徐庶 were friends of Si Ma Hui (not students), while another claims there were 5 geniuses and not 7. Regardless of the legends, Si Ma Hui did indeed exist and is widely regarded as the bridge connecting Liu Bei to Zhu Ge Liang. His grave has even been found.
Si Ma Hui Wiki