Seniyad is a Druid in Baldur's Gate. and a protector of the forest. According to Izefia, a Shadow Druid deeper in Cloakwood forest, a potential companion Jaheira is a follower of Seniyad, who is an arch druid - one of three - with a pacifist doctrine.
When you talk to Aldeth Sashenstar in the first Cloakwood area, he will ask for your protection. If you agree, Seniyad and several other druids will appear and ask you to move out of they way so they can kill Aldeth. Complying will cause Aldeth to attack you. Refusing will cause Seniyad to attack you, unless Jaheira is in your party.
Bug?: In some versions, Seniyad may attack even if Jaheira is in the party.
Aiding Aldeth enables you to access the otherwise impenetrable Merchant League Estate building in Baldur's Gate.,
His three Druid allies cast Flame Blade and melee attack.