Courtney Krieger is a probie and also an FBI Special agent who appeared in the Season 5 episode, Identity Crisis (episode).
Kreiger was the head of a solo operation in the field which involved keeping an eye on Marvin Hinton aka Fredrick LeClaire, a career criminal who had recently been released from prison and had his original identity erased.
However things went horribly went wrong when Hinton was murdered by having mercury injected into his brain and his body eventually ended up in the custody of NCIS, prompting a murder investigation to be opened with the investigation being a joint one between both NCIS and the FBI.
Not much is known about Kreiger's past only that she is a new FBI Agent and it was also revealed that Tobias Fornell is also her boss.
She has also mentioned that she has some prior experience in terms of going undercover.
Eager to please, Kreiger is essentially a Probie, not realizing her mistakes can sometimes anger her superiors.
Despite this, she shows some determination which is demonstrated when she beats up Robert Graves, a possible suspect with links to Kamal Konkani, a terrorist believed to be responsible for creating new identities for terrorists.