What does "I worship the Lord of the Thunderbolt" mean, in a translation of Shantideva's Bodhicaryavatara? Quoted below is from  Shantideva's Bodhicaryavatara.


  I cry aloud, looking for protection.
  And I worship the Lord of the Thunderbolt. When they have seen him, 
  the messengers of death and the other evil beings are frightened and they flee to the four directions.
  I now go terrified to you for refuge—after having neglected your instruction, 
  because of beholding fear. May you quickly extinguish fear. 


What is the Buddhist explanation of this text?  

Considering the list of excellence such as compassion, wisdom etc. mentioned prior to this text in the form of Bodhisattva, is it right to understand this as a personification of courage? or is it literally worship of the Lord of the Thunderbolt, be it Zeus or Indra, to extinguish fear?
I would think it refers to the author's main Vajrayana teacher. As ChrisW rightly notes: Thunderbolt is a translation of Vajra. the lord The student-teacher relationship is very important in Buddhist tantra and Santideva was an Indian practitioner of Buddhist tantra. 

There are several reasons to think that it refers to his personal teacher:
1) in tantra one is supposed to see the teacher as one with the highest Buddha 
2) in the text here it says that the author has neglected 'his instructions' - that is, the instructions of the Lord of the Thunderbolt. That makes most sense if it does refer to his personal teacher.