Why do some closing credits show the character name of only one actor?

Question

In some closing credits, one (*) actor is listed with the name of her/his character in addition, in the form: [Actor name] as [Character name].

I always thought this is the case for actors playing characters that are disguised (e.g., in monster costumes), or for actors that only gave their motion capture/voice (e.g., for digitally created characters).

For example (not the best example, as it contains a "Featuring" in addition), in The Lord of the Rings: The Return of the King (see video, at 3:31):

Featuring
Andy Serkis
as Gollum

Ah, The Hobbit: An Unexpected Journey contains it without "Featuring" (see video, 1:25):

Andy Serkis
as Gollum

But then I saw The Hobbit: The Desolation of Smaug, and if I remember it correctly (couldn’t find the credits online), it read:

Orlando Bloom
as
Legolas

Now this refutes my theory. Orlando Bloom is not acting disguised nor is he a digital creation.

What is the reason for this?

(* Maybe there are credits where this applies to several actors, but I noticed it only for exactly one actor so far.)

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(Note that the question Why do some actors in credits appear as - Character (As Actor) may look similar, but that one is about the IMDb.)

Answer 1

There's a bit of prestige being listed last. Generally this spot is for a famous actor that has a small role. For the Hobbit movies, Bloom isn't in all the films so he won't get the same type of billing as the regular players. The SAG rules are different for guest stars and featured players than for principal players. For Andy Serkis, I think it's because he's a featured player, for Orlando Bloom it's because he's a guest star. Both actors are famous, but neither are principal players.

From the Wikipedia article about "billing":

An actor may receive "last billing", which usually designates a smaller role played by a famous name. They are usually credited after the rest of the lead cast, prefixed with "and" (or also "with" if there is more than one, as Samuel L. Jackson was in the latter two Star Wars prequels). In some cases, the name is followed by "as" and then the name of the character (sometimes called an "and-as" credit). This is not the case if that character is unseen for most of the movie (see Ernst Stavro Blofeld).

An early last billing credit in a film's opening simply listed a question mark (?) as portraying the monster in the 1931 classic Frankenstein, which still lists it that way today, although the reissued prints seen today add actor Boris Karloff to the end credit listings, as the film made him a huge star such that the credits of the film's first sequel The Bride of Frankenstein credits him only by his last name.

One of the first "and-as" credits was afforded Spencer Tracy (as Lieutenant Colonel James H. Doolittle) in the 1944 World War II film Thirty Seconds Over Tokyo, since another top box office star of the time, Van Johnson, had top billing and Tracy was too big a star to receive second billing.

Some films have both an "and-as" credit and a separate last billing credit, such as the Irwin Allen 1978 disaster film The Swarm, the opening credits of which, after listing an already large cast of stars, concludes with "Fred MacMurray as Clarence ... and Henry Fonda".

Answer 2

I thought it was because it was a better known or more popular actor. I was watching One Day at a Time reruns and noticed the last credit said "Valerie Bertinelli as Barbara Cooper"; this happened after Valerie became more popular. I noticed that on a few other TV shows also.