Horrigan is a huge man-like armored figure., born in in 2211. Originally a Secret Service Agent for Enclave President Dick Richardson, Horrigan was sent out with several other teams to search for slaves for use in excavating the remains of the Mariposa Military Base. In September of 2236, scientists unearthed the F.E.V. and mutations began to occur amongst those who come in contact with it, including Horrigan, who was quickly transported back to the Enclave for further research.
Sometime between 2236 and 2238, Frank Horrigan underwent his transformation into a super mutant. During this period, he was kept under heavy sedation and operated on by Enclave technicians and scientists under the directions of Dr. Charles Curling. Following testing in January of 2239, it was decided that Horrigan should be activated for field operations.
After a series of successful and bloody missions ending in March of 2239, the Enclave created a modified version of power armor specifically to encapsulate Horrigan's bulk. From this point forward, Frank was "married" to his suit. He could not be separated from it as it continually pumped him full of drugs, acting as a "life support."
Horrigan was eventually defeated in 2242 by a tribal known as the Chosen One. Despite being literally torn in half at the waist, Horrigan was able to gather enough strength for some final words. Though he claimed to have activated the Enclave Oil Rig's self-destruct mechanism, this appears to have actually been a bluff. The reactor meltdown triggered by the Chosen One destroyed the oil rig and all traces of Frank Horrigan.
Horrigan is a mutant, but he had been a monster before his exposure to FEV in the military base, as he had many psychological problems. It is important to note that Horrigan never considered himself a mutant; only the scientists at the Enclave would have considered him one, but they mostly referred to him as an "experiment", and even then, not to his face. Most soldiers considered Horrigan a walking nuke, something the tech boys built, and they were not generally aware of his mutant status. Most did consider him a freak and there were few soldiers who wanted to accompany him on missions.
Horrigan's loyalty to the Presidency, the Enclave, and the armed forces was present before his exposure to FEV, and it was reinforced by Presidential Directive through various conditioning and testing programs developed by the Enclave. Horrigan's low Intelligence (which was further damaged by the FEV exposure) made these conditioning programs take root easily.
Standing more than 12 feet tall, Horrigan is significantly taller and bulkier than a standard super mutant. His FEV mutation was further augmented with controlled injections of an experimental modified version of FEV developed by the Enclave, resulting in Horrigan being a "next-gen" super mutant... stronger, faster, tougher, and just plain meaner. Additionally, a special suit of power armor was cybernetically grafted onto his body, transforming him into a walking death machine without peer. Cybernetic elements include bionic eyes, arm control mechanisms and leg rotators.
Although of generally low intelligence, Horrigan noticeably lacks the simple-minded "moronic" mental deficiencies that commonly plague many super mutants such as Harry. For example, Horrigan speaks in complete sentences, using normal grammar and vocabulary, and generally lacks any obvious signs of mental deficiency. Horrigan most likely mimics the speech and mannerisms of his Enclave creators and propaganda programs he heard.
Horrigan has 999 HP, and is equipped with two unique weapons normally unobtainable, an End Boss plasma gun and an End Boss knife. He is also very fast, having a great amount of AP (being able to attack several times per round). If his weapons are disabled (either due to running out of ammo, or if his limbs are crippled by repeated aimed shots) Horrigan will hand-to-hand combat with his enemies to the death. Normally, he continually fires his gun until he runs out of ammo, at which point he changes for his knife.
Additionally, Horrigan's armor grants him high resistance against small arms fire, explosions, and laser and plasma bolts, but is somewhat vulnerable to electricity. This special cybernetic armor cannot be bypassed even by critical hits, which makes him extremely hard to kill, even relative to his high number of hitpoints.
With a save editor, Horrigan's personal weapons can be obtained.
His armor is like a protective and defensive survival armor directly grafted to his body. It is part of the skin of Frank Horrigan (like the super mutants' armor of Fallout and Fallout 2), and is therefore not an item.
The mutagenic serum does not work on Horrigan, as he is not an average mutant.
Once defeated, he will engage in dialogue, without legs and crawling on his arms, before dying.
Some NPCs claim that the mutated toe is a one hit K.O. device for destroying Frank Horrigan, but it is merely a myth.
Though he has placeholder graphics for both reactions, Horrigan is the only character with a talking head that cannot be impressed or made furious.
If blinded, he switches from the plasma gun to his knife.
When killed, he appears as a new entry in the Pip-Boy 2000 kills section. His section is named 'Big Bad Boss Kills', and within it, he is described as a "genetically engineered total homicidal maniac cyborg bodyguard".
"Dumping the F.E.V. toxin into our air doesn't make you a hero. You're just another mutant that needs to be put down. Making our reactor melt-down means things are going to be pretty hot in here soon. Pity you won't live long enough to see it. You're not a hero, you're just a walking corpse.""
(Defeated) "You (cough), you haven't won here. You and your mutie-bastard friends are gonna join me in a big ol' mushroom cloud sendoff. I just triggered the self-destruct. (Heh, heh; cough, cough,...) The work will go on. You didn't do nothing here, 'cept seal your own death warrants. Duty, (cough) honor... courage... Semper Fiiiii........"
He was named after Clint Eastwood's character in the film In the Line of Fire. Frank Horrigan from the movie was also a secret service agent whose task was to protect the US president.
In his last words Horrigan uses the phrase Semper Fi. Semper Fi is short for Semper Fidelis which is Latin for "Always Faithful" and is the motto of the United States Marine Corps. Horrigan using this phrase also helps to show the link between the Enclave and the pre-War military, and to show that he has always done his duty for his country, no matter how he did it.