Actor

Actors are people who act. Actors can be any participants in events, in a wider sense of the word, but usually the term refers to performers of works of fiction, or dramatised events, reenactments, etc. That is, people who play roles for the purpose of entertaining others (who are spectators).

"Actor" is an English word that is still marked when the occupation refers to women's work. Thus "actor" as a generic (i.e., gender-neutral) category is belied by the common use of the word "actress", and, reciprocically, women who act are made invisible by use of the word "actor" as a specific term referring to male actors.

The actors who perform works for the stage, television or film (etc.) have a substantial impact on the meaning of those works, because their interpretations transform the stories, as they were written, before they reach the audience.

In many cases, they also share their input with the creators of those works, which, especially in the case of ongoing projects where the characters the actors play receive new material, can influence the direction of the growth of those characters.

Conversely, if an actor whose work has been closely linked to a specific role ceases to play that role, for whatever reason, this can effectively terminate the character as well.

Examples of the impact of actors on works of SF

Health

• The role of the Doctor (Doctor Who) has been carried on by integrating the replacement of actors into the character's storyline, following the decline in the health of William Hartnell, who originated the part.
• Virginia Hey's health suffered from the makeup she had to wear as Zhaan, which led to her being written out of Farscape.

Pregnancies

Pregnant actors can create both complications and opportunities in storytelling, especially on television.

• Gillian Anderson's first pregnancy led the makers of The X-Files to invent an adbuction storyline for her character, Dana Scully.

Legal problems

• Michelle Rodriguez and Cynthia Watros' arrests for driving under the influence of alcohol were apparently only coincidental with the fate of their characters on Lost.

Direct input

• Tricia Helfer's suggestions regarding Number Six on Battlestar Galactica (2004 TV series).

Same actor, different character

In some cases an actor remains on a television series while playing a different character than they did before.

• Personality erasure, wherein a character's identity changes, but the part does not require a new character with a distinct "body".
• Multiple roles, sometimes requiring special effects or body doubles, to allow one actor to play against herself. Lucy Lawless did this many times on Xena; Alyson Hannigan played a vampire Willow from a parallel universe, and Nicholas Brendon also played two Xanders in the one episode (with help from his twin brother).
• Personality swaps, often for comedic effect; see, e.g., when Faith & Buffy switched bodies; when Callisto & Xena switched bodies; "Out of Their Minds" on Farscape.