Chadwick
You may also be looking for actor Robert Chadwick.
Chadwick was an operative with Starfleet Intelligence in 2374.

In that capacity, he enlisted Miles O'Brien to infiltrate the Orion Syndicate on Farius Prime. Chadwick, who himself had been on undercover assignments in the past, tasked O'Brien with identifying a leak within Starfleet, who had been informing the Syndicate as to the identities of Starfleet Intelligence undercover operatives. 

Although O'Brien managed to complete his assignment, he also discovered that the Syndicate had begun working with the Dominion in a conspiracy to destabilize the Klingon-Federation alliance. Upon learning this, Chadwick decided to warn the Klingons about an assassination plot against their ambassador to Farius, a decision which would lead to the deaths of the Syndicate members with whom O'Brien had become acquainted. 

O'Brien, however, who had become close to Syndicate member Liam Bilby, chose to disobey orders and warn Bilby of the plot, incapacitating Chadwick in order to do so. Bilby refused to abandon the plot, however, knowing that to do so would let the Syndicate know that he had brought an infiltrator into their midst, ensuring the death of his family. Despite O'Brien's disobedience, Chadwick, who was sensitive to the dangers of working undercover, chose not to mention it in his final report. ()

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Humans
Starfleet personnel (24th century)