Cooperator (noun)

1. A person who willingly works together with others, especially in a joint effort to achieve a common goal or objective.
2. A person who is willing to collaborate and assist others in order to achieve a common goal.

Origin:

From the latin word "cooperatorem", meaning "one who works together" and "ist" which is a suffix indicating a person who practices or is an expert in a certain activity.

Examples:

1. He was a great cooperator and always willing to help his colleagues.
2. She was a natural cooperator and always helped out with group projects.
3. He was a reliable cooperator who always contributed to the team's success.
4. She was a very good cooperator and always supported the team's efforts.
5. He was an excellent cooperator and always helped to create a positive working environment.