The Brothers of Thunder, and their sister organization The Sisters of Thunder are a militant Paladin order of worshippers of Donar. These paladins fight with war hammers, and gain special access to lightning based spells.
Paladins of this order may add the following spells to their spell list, so long as they retain Donar's favor.
Spell Level
1) Shock Shield
2) Defensive Shock
3) Sheet Lightning
4) Chain Lightning
Furthermore Paladins of the Brothers/Sister of Thunder who choose the divine bond ability replace Flaming, and Flaming burst for Shock, and Shocking Burst. And add Thundering, to the list of abilities they may choose.
Paladins of Thunder almost always choose the weapon bond divine bond, rarely ever bonding with a mount. Most fight with War Hammers, though light hammers and shields, or even dwarven long hammers are not unheard of.