If you were lucky (err... unlucky) enough to find your way onto the level  "You're Wormfood, Dude"  you will find a terminal with the following text.

I am Arther Frain, Chief Petty Officer, USEC 
Marathon.
Arther Frane calling all USEC personnel
Calling Cmdr. Robert Blake...
Calling Security Chief Jones...
Arther Frain calling any USEC controlled ship 
in vicinity...

Station hull breached, we are losing 
pressurization.  More than half the men are 
without vacuum suits.  Patrols reporting 
intruder, last location unknown.

Any USEC controlled ship surviving nova event, 
transport when ready.

Arther Frain calling.
That is all...

A strangely haunting terminal. Oddly the spelling of the name 'Arther Frain' changes to 'Arther Frane' in one part of the text. Also the name 'Arther' is a less common form of the name 'Arthur'.

The opening part  "I am Arther Frain"  comes from the opening dialogue in the John Boorman film 'Zardoz'.

After the release of Marathon Infinity Greg Kirkpatrick made numerous references to being "Arthur Frain" (the puppet master). Note that Greg used the more common form of the name 'Arthur' this time.

On IRC #duality on January 24, 1997 Greg Kirpatrick (toolboi) and Randy Reddig (ydnar).

toolboi is arthur frain
toolboi: me is the puppetmaster
toolboi is the puppetmaster
ydnar: the film zardoz has had significant influence on the doubleaught psyche

On IRC #marathon on January 28, 1997.

toolboi: I am arthur frain.
toolboi: I am the puppet master

On November 13, 1997 Greg Kirkpatrick posted a list of what he described as "good" science fiction movies. On his list was Zardoz. Greg wrote:

Zardoz (i am aurthur Frain.. iam the puppet master..)

Zardoz is a 1974 film of a dystopian future set in 2293.

The film begins with a prologue. An actor's disembodied head appears on a black screen and (breaking the fourth wall) speaks to the audience setting the scene for the movie.

Below is the prologue text from the script of the movie.

I am Arthur Frayn, and I am Zardoz.
I have lived three hundred years and I long to die but death is no longer possible.
I am immortal.
I present now my story, full of mystery and intrigue, rich in irony and most satirical.
It is set deep in a possible future so none of these events have yet occurred.
But they may.
Be warned lest you end as I.
In this tale I am a fake god by occupation and a magician by inclination.
Merlin was my hero.
I am the puppet master.
I manipulate many of the characters and events you will see.
But I'm invented too for your entertainment and amusement.
And you, poor creatures, who conjured you out of the clay?
Is God in show business too?

You will note that in the script the speaker is called Arthur Frayn.

I had the opportunity to ask Greg Kirkpatrick (toolboi) about the spelling differences on IRC #duality on November 26, 1996. Here's a log of the conversation:

Godot: whats the deal with Frane and Frain
Godot: ?
toolboi: hmmmnn
Godot: spelling
toolboi: you mean the phonetic vs other spelling
toolboi: i just spelled it phonetically... 
Godot: actually it should be Frayn
Godot: going by the credits
Godot: I saw
toolboi: i think that in the movie it's actually written out once or twice.. 
toolboi: right
toolboi: oops
toolboi: whatever.. it's not the real aurhur frain
toolboi: that terminal is pretty hard to find, i hope
Godot: true he's Arther Frane, Arther with an E
Godot: Not a U
toolboi: cool. i got part of it right, then
Godot: :-)
Godot: whatever
toolboi: when i saw arther spelled with an 'e' on your page, i thought i'd screwed up...
toolboi: i knew that i mispelled frayn, but i thought it was really spelled "frain"
toolboi: :)
Godot: err... 
toolboi: hamish i gotta get back to work... duty calls

And with that he disappeared... Phhht! Just like that

Phonetic spelling seems to be a thing in the Marathon series. Some names are spelled differently throughout out all three games, even within games and even within terminals.

And Greg is not the only one to spell Arthur Frayn's name phonetically.

For example Steve Mizrach <seeker1@anthro.ufl.edu> at the Department of Anthropology, University of Florida, had this to say about the film back in January 24, 1996. (The original link is long gone.)

In this film Frane creates the realities that many characters within the film experience. At the same time Frane is part of a reality that Boorman has created for the viewer to experience. Frane asks the question of whether Boorman and we viewers are not part of a reality for some other being to experience. Here we raise the question of multiple realities. Multiple realities are nothing new to cultivation (Gerbner & Gross, 1976) or social reality theory (for reviews, see Hawkins & Pingree, 1982; Ogles, 1987) researchers. Each of these realities have rules, practices, or protocols that must be followed. These rituals must be followed or the individual can no longer remain a member of that society, that culture, or that reality.

To say that Zardoz is an odd film is an understatement. At one level it explores the concept of immortality and basically concludes that it is not all it's cracked up to be.

The title Zardoz is a portmanteau word made up from the title of L Frank Baum's book 'The Wonderful Wizard of Oz'.

In the film the protagonist Zed (Sean Connery) finds this out when he discovers the book in an old library. The floating stone head of the God Zardoz is nothing more than the man behind the curtain in the The Wizard of Oz (the pupper master).