The Aegis of the Immortal drops from Roshan and brings it's carrier back to life with full health and mana at the spot he died. It is one of the items which decides the outcome of the match and when strategically used can win otherwise hopeless game. The Aegis is removed from it's owner inventory after it has been used or five minutes after it has been picked up which triggers full mana and health heal.
Roshan snatched the Aegis of the Immortal from one of the Shop Keepers. Roshan has been cursed, so that his life and precious treasures are stolen repeatedly.
Effect of the Aegis (October 27th, 2014 Patch)
Brings back the owner of the Aegis back to life with life with full health and mana 5 seconds later at the location where he died. If Aegis is not used it disappears from the inventory of the carrier 5 minutes later, healing the carrier and restoring full mana over 5 seconds.