17 Celebrities You Never Knew Guest Starred On NCIS

In season nine, this famed actress plays a Department of Defense member and an ex of Gibbs'.

The Two and a Half Men actor is potentially a recurring character in this upcoming season as a Navy captain and doctor.

In seasons nine and ten, West Wing fans can see "Toby" appear as a terrifying CEO.

Tom Hanks' son appeared in two episodes in seasons ten and eleven as a Department of Defense investigator.

The Star Wars actor appeared in seasons ten and eleven as Gibbs' father's best friend.

The Pretty Little Liars star played Timothy McGee's sister and appeared in a handful of episodes early in the show's run.

Best known for being in Twin Peaks, Fenn played a seemingly innocent Jane Doe in the first season.

The Castle stars starred in different episodes, with Dever portraying a sketchy bartender in season four and Huertas appeared in season six as a Marine.

In season eight, Newhart plays Ducky's predecessor and mentor.

In season four, the Supernatural actor played a man with a bad rep who was suspected of kidnapping.

Veteran actress Tomlin plays McGee's grandmother and a peace activist in season nine.

Diggs plays a wounded Marine in one of the episodes of season 13.

In the season 2 premiere, Breslin portrays a young, blind piano prodigy.

In season three, Efron played a teenager that purchased a cell phone he really shouldn't have...

The Modern Family actor played a rather suspicious security guard in season six.

A season 13 episode featured the Arrested Development actress as an author.

The Lost and Once Upon A Time star appeared on a season one episode.