the thunder king is a mogu who tore the heart of a titan watcher out. that gave him power over lightning (
"It is said that he tore out the very heart of the mogu God. And from that hateful act he gained power over wind and storm.", datamined info).
he used that power to rise to power and become the mogu king ("
The Thunder King rose to power the “the mogu way,” namely by eliminating his rivals one by one. According to legend he was able to accomplish this with the help of a mysterious artifact that he found in the depths of a mountain.").
in the year 170 of the thunder king's reign, the korune clan gave him the divine bell, made with "maker's flesh" (probably Ra-den's, since he's the titanic watcher the mogu have in their possession) and the "breath of the darkest shadow" (sha). the thunder king used the divine bell to control the sha, empowering his troops with anger and hatred, and causing fear and doubts on his enemies.
"In the one-hundred-and-seventieth year of the Thunder King's reign, the
Korune spellweavers (casts "Sha Bolt and Sha Eruption") came to Lei Shen with their greatest creation.
A bell cast from the makers' flesh, shaped by stars' fire, and bound by the breath of darkest shadow. This bell, when rung, could shake the world and call to the heavens.
Taken to war, the bell's cacophonous tones stirred the hearts of Lei Shen's warriors. It fueled their hatred and anger, lending them strength on the field of battle. The bell's screaming voice struck fear and doubt into the hearts of the Emperor's enemies, sending them fleeing in his path.
Awed by its power, the Thunder King described the instrument as "the voice of the gods," and named it Shenqing, the Divine Bell." (
http://www.wowpedia.org/Ancient_Korune_Tablet)
so yeah, I'd say we know enough of the thunder king.
the korune clan mastered the sha, made a "sha remote control" and gave it to the thunder king as a gift 170 years after he became the emperor by stealing titan power.