How do you unlock all crackdown agents?

To unlock all Crackdown agents in the game "Crackdown," you need to complete specific challenges associated with each agent. Each agent is tied to different types of orbs and missions, such as collecting agility orbs or completing story missions. As you progress and reach certain milestones, the agents will become available for recruitment. Focus on completing the main missions and exploring the city to gather the necessary orbs efficiently.