Tara was absorbed into the Buddhist pantheon of deities in the 6th century AD from Hinduism.  There are numerous forms of Tara, the most popular being Green Tara and White Tara.  

Green Tara is invoked for protection from fear and the eight obscurations: lions (pride), wild elephants (delusion/ignorance), fires (hatred/anger), snakes (jealousy), bandits and thieves (wrong views), bondage (avarice/miserliness), floods (desire/attachment) and evil spirits and demons (deluded doubts).  White Tara is invoked for longevity and healing.

Their importance in Tibet is reflected in the story that they manifested as the two wives of the first Buddhist king of Tibet, Songstan Gampo (618-649 AD). The first wife, the Nepalese Princess Bhrikuti was said to be an incarnation of Green Tara; the second wife, the Chinese Princess Wencheng, was said to be an incarnation of White Tara.