First officer

Aboard a starship the first officer or executive officer (or XO) was the second-in-command, just below the captain. 
== Duties ==
In Starfleet, the position was usually held by an officer with the rank of commander or lieutenant commander, but exceptions do exist, such as with Sylvia Tilly in the 32nd century. 
In Starfleet's early period of existence, the first officer would accompany the captain on landing parties, depending on the situation. By the 24th century, however, it was the first officer who usually led away teams while the captain remained on the ship.
In the 22nd and 23rd centuries, the first officer served as a department head first and the executive officer second (similar to the second officer and third officer) and only took command when the captain left the bridge, as such, there was no first officer's station as there would be in the 24th century, as the XO would alternate between the command chair and their station as a department head.
Noted functions of the first officer aboard a Federation starship were:
* The primary role of the second-in-command was to carry out the decisions of the Captain. ()
** Obey and implement the captain's orders. (; ; )
** To be informed, insomuch as to know everything the captain knew. () As well as had full security clearance to possess such knowledge. ()
** Attending important meetings and briefings with the captain. ()
** Take command of the vessel in the event of the captain's absence, incapacitation or death. (; , ; )
* To point out any actions that may be mistakes by a commanding officer. (, ; , , , , )
* To safeguard the lives of the ship's crew, particularly the captain. ( )
* Act as the officer in charge of personnel. ()
** Preparing and issuing duty rosters. () 
*** Following the promotion of Acting Ensign Wesley Crusher in 2364, Captain Jean-Luc Picard told Crusher, that while he waited for his acceptance into Starfleet Academy, "you will learn this ship–every operation, every function," and that Commander William Riker would prepare a duty schedule for him, "heavy on study". ()
*** According to Captain Kathryn Janeway, if a member of the crew needs to leave their post, they are required to inform the first officer. ()
** Coordinate personnel transfers between departments. ()
** Working with the chief medical officer or counselor on crew evaluations, () as well as crew discipline. ()
** Supervise subordinates.
*** When Hoshi Sato requested the help of T'Pol, Sato expressed her frustration with how frequently T'Pol was looking over her shoulder, double-checking her log entries, and translations. While T'Pol felt she was just doing her job, and explained how she held Sato to a high standard because "I know you're capable of achieving it." ()
* Managing the ship's resources, including systems allocation. ()
Aboard a Klingon warship, the first officer served the Captain, but stood for the crew. They also reviewed and kept the ship's record of battle. ()
== Noted first officers ==
=== 22nd century first officers ===
File:T'Pol, early 2154.jpg|Commander T'Pol ()
=== 23rd century first officers ===
File:George Kirk.jpg|Lieutenant George Kirk () 
File:Una Chin-Riley, 2253.jpg|Cmdr. Una Chin-Riley ()
File:Michael Burnham.jpg|Cmdr. Michael Burnham ( and )
File:Saru, 2257.jpg|Cmdr. Saru (USS Discovery)
File:James T. Kirk, 2259.jpg|Lieutenant James T. Kirk ()
File:Tom Nellis.jpg|Lieutenant Tom Nellis (Antares)
File:Spock, 2268.jpg|Cmdr. / Capt. Spock (USS Enterprise and )
File:Will Decker.jpg|Cmdr. Will Decker (USS Enterprise)
File:Pavel Chekov, 2285.jpg|Cmdr. Pavel Chekov ()
=== 24th century first officers ===
File:William Riker, 2366.jpg|Commander William T. Riker (, , and )
File:Kira Nerys, 2375.jpg|Colonel Kira Nerys (Deep Space 9 and )
File:Worf, 2375.jpg|Lt. Cmdr. Worf (USS Defiant and )
File:Benjamin Sisko, 2366.jpg|Lt. Cmdr. Benjamin Sisko ( and )
File:Elizabeth Shelby, 2367.jpg|Cmdr. Elizabeth Shelby (USS Enterprise-D)
File:Christopher Hobson.jpg|Lieutenant Commander Christopher Hobson ()
File:Cavit.jpg|Lt. Cmdr. Cavit ()
File:Chakotay, 2377.jpg|Commander Chakotay (USS Voyager)
File:Jack Ransom.png|Commander Jack Ransom ()
File:Adreek-Hu.jpg|Commander Adreek-Hu ()
File:Tysess.jpg|Commander Tysess ()
File:Cristóbal Rios, 2390.jpg|Cristóbal Rios ()
=== 25th century first officers ===
File:Annika Hansen, 2401.jpg|Commander Annika Hansen ()
File:Moshe.jpg|Commander Moshe ()
File:Raffaela Musiker, 2402.png|Commander Raffaela Musiker ()
=== 29th century first officers ===
File:Ducane.jpg|Lieutenant Ducane ()
=== 32nd century first officers ===
File:Patrick Fickett.png|Commander Patrick Fickett ()
File:Michael Burnham, Commander, 3189.png|Commander Michael Burnham (USS Discovery)
File:Saru, 3190.jpg|Captain Saru (USS Discovery)
File:Commander Rayner.png|Commander Rayner (USS Discovery)
=== Alternate reality ===
File:George Kirk at post.jpg|Lieutenant George Kirk
File:Spock (alternate reality).jpg|Commander 
File:Kirk first officer.jpg|Commander 
=== Mirror universe ===
File:Jonathan Archer (mirror).jpg|Commander Jonathan Archer
File:Keyla Detmer, mirror.jpg|Keyla Detmer
File:Spock (mirror).jpg|Commander Spock
== List of first officers ==
=== Starfleet ===
*Commander Brink
** (2367)
*Lieutenant Maxwell Burke
** (2370–2376)
*Ensign Sylvia Tilly
** (3189)
*Lieutenant Commander Data 
**USS Enterprise-D (2369) 
*Commander Flaherty
** (2365)
*Commander Steven Mullen
** (2167)
*Christopher Pike
**USS Enterprise (2240s–2250)
;Unnamed:
* Pegasus first officer
** 
* Phoenix first offcier
** 
=== Klingon Empire ===
*Hon-Tihl
** (2369)
*Kaz
** (2269)
*Korax
** (2267)
** (2269)
*Commander Kurn
**USS Enterprise-D (2366, part of the Officer Exchange Program)
*Lieutenant Commander Worf
** (2373 – 2375)
** (2375)
=== Other ===
*Human – Matthew Ryan
** (2151, demoted in August to able crewman)
*Ferengi – Kazago
**Bok's Marauder (2364)
*Tellarite – Gaavrin
**Tezra (early 22nd century)
*Tygarian – Romah Doek
** Nanut
*Romulan – 
* Romulan – Ayel
** Narada
=== Mirror universe ===
*Commander 
** (2155)
*Lieutenant Commander 
** (2155)
*
** (2257)
*Commander 
** (2267)
=== Alternate timelines ===
*Lieutenant Sato
**Enterprise NX-01 (2165)
*Commander Thelin
**USS Enterprise (2269)
*Commander Worf
**USS Enterprise-D (2367 – 2370) 
*Commander 
** (2258 – 2263)
** (2263)
** (2260s)
*Commander 
**USS Enterprise (2258, 2259)
== Appendices ==
=== Apocrypha ===
*Acting First officer 
** (Desperate Hours)
*Commander Jon Cooper
**Starbase 47 (Star Trek: Vanguard)
*Commander Sonya Gomez
**USS da Vinci (Star Trek: Starfleet Corps of Engineers)
*Commander Elizabeth Shelby
** (Star Trek: New Frontier)
*Lieutenant Commander Demora Sulu (2301 – 2311)
** (Star Trek: The Lost Era)
* Commander Christine Vale 
** (Star Trek: Titan)
*Commander Elias Vaughn (2376 – 2379)
**Deep Space 9 (Star Trek: Deep Space Nine (Pocket))
**USS Defiant
*Commander Worf
**USS Enterprise-E (2380)
===External link===
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