Thinking Cap is a sacred unique Skull Cap.
A good option for casters early on, being easy to find due to being a lower quality level base item. The + to all skills, spell damage, and maximum mana increase are all beneficial for casters.
Defense: (1429-1562) to (1472-1605)
Insert which items or affixes that have great synergy with this item here.
For patch notes, item changes, and miscellaneous information.
An item of the same name exists in Diablo I.