The four core characteristics of an AI agent are:

1. Autonomy: The ability to operate and make decisions independently without constant human intervention.
2. Perception: The capability to sense, interpret, and understand the environment it operates in through various sensors or data inputs.
3. Goal-oriented or proactive behavior: Having explicit objectives and the ability to take initiative to achieve those goals, adapting as situations change.
4. Learning: The capacity to learn from past experiences and improve performance over time using methods like machine learning or reinforcement learning.

These characteristics enable AI agents to function intelligently and effectively in dynamic environments, making decisions, responding to changes, and improving their capabilities continuously.