1. Government Conspiracy: Bourne was originally a highly trained CIA assassin known as "David Webb." However, after a rogue operation went wrong, he suffered amnesia and became a civilian with no memory of his past. The CIA and other government agencies seek to eliminate him to cover up the secrets of the Treadstone program, a clandestine black ops project that created Bourne and other assassins like him.
2. Blackbriar: Blackbriar is a successor organization to Treadstone, formed by former CIA officials. They want to control Bourne and use his skills for their own clandestine operations. However, Bourne becomes a threat to their plans because of his independent nature and the risk of exposing their activities.
3. Kirill and the Russian Government: In some instances, Bourne's actions come into conflict with the interests of the Russian government, specifically the character Kirill. Kirill is a high-ranking Russian intelligence officer who wants revenge against Bourne for past actions that involved the death of loved ones. He considers Bourne a personal enemy and seeks to eliminate him.
4. Personal Enmity: As Bourne uncovers the truth about his past and the conspiracies surrounding him, he encounters individuals who develop a personal vendetta against him. These individuals could be former colleagues or enemies who feel betrayed or wronged by Bourne's actions, motivating them to seek revenge.
It's important to note that the reasons for wanting to kill Bourne vary depending on the specific plotlines of the Bourne series books or movies, and not all of these reasons may be present in every story.