Keeper of the Light is a ranged intelligence support hero with a huge area of effect damage ability and essentially unlimited mana for himself and allies, making him a popular support pick in concert with mana-hungry laners as well as a strong anti-pusher.
Skills
Illuminate is usually skilled and maxed first.
Mana Leak is usually skilled last and always maxed last.
Chakra Magic is usually skilled second (sometimes first if laning with a good single target nuker), and maxed second.
Spirit Form is always skilled (levels 6, 11 and 16).
Items
Starting Items: Courier and/or Observer Wards, Tangos, Healing Salve, 3x Iron Branches.
Early Game: Observer Wards, Flying Courier, Boots of Speed, Magic Wand, optional Bracer.
Core Items: Tranquil Boots, Mekanism.
Luxury Items: Aghanim's Scepter, Drums of Endurance, Boots of Travel, Force Staff, Heaven's Halberd, Scythe of Vyse, Shiva's Guard.
Situational Items: Sentry Wards, Dust of Appearance, Gem (vision), Smoke of Deceit (ganking), Vladmir's Offering (melee cores), Pipe of Insight (if didn't buy Mekanism), Necronomicon (pusing), Rod of Atos.