Darksteel Shield

Darksteel Shield is a large shield +4 which provides an armor class bonus of 5, which requires 15 strength to wear it. It also provides 10% resistance to fire, cold, acid and poison. This item appears in Baldur's Gate II: Throne of Bhaal, it's the most powerful shield available. The shield can be found in Sendai's Enclave, when you kill the Priestess in service of Sendai.

In-game description
"Fashioned from dwarven darksteel, this heavily enchanted shield provides more protection than most suits of armor. Legend holds that it was meant to be presented as a gift to the dwarvish hero Glimred Heavyhand, but he disappeared on his ill fated quest into the bowels of the Marching Mountains before the work was completed. With Glimred gone, the shield was sold to the highest bidder - though the dwarven smiths refused to divulge the mysterious buyer's identity."