Stoat Muldoon is a major comic antagonist in the Butt-Ugly Martians franchise. He is the host of the afternoon TV show Muldoon: Alien Hunter, filmed out of his home (a converted missile silo in the Mojave Desert), in which he informs the audience of the presence of a "dangerous" alien presence on Planet Earth. While he is looked at by most (including the Martians' human friends, oddly enough) as a crazy conspiracy theorist pedaling nonsense, he turns out to be correct in his assertions, and dedicates his life to ridding the planet of its new "dangerous" visitors.
While Muldoon possesses a large variety of advanced technology and weapons meant to deter extraterrestrial threats, he is not looked at as much of a threat by the Martians or their friends, who often use him as their butt monkey on whom they sic actual threats while they try to think of a real plan. Despite his haplessness, Muldoon sees himself as a great hero due to his overinflated sense of self-importance; and constantly talks about himself in the third person using grandiose, boastful language.
On the original Butt-Ugly Martians TV show, Muldoon is voiced by Robert Stack, in what would sadly be one of his final projects. Leaving aside what perfect casting this is (from an in-joke perspective, at least), Stack works well in the role, bringing the perfect feeling of delusion and pompousness that a character like this would need. He also kind of has that "radio delivery" thing going, where he sounds like he's recording for a '50s radio serial; which I think is a great touch for a character who essentially sees himself as a planet defending superhero.
For the show's tie-in game Zoom or Doom!, Robert was unable to reprise his role (likely due to age, prior commitments, and his fading health), so Geoff Pierson was called in to host in his place. Going by his other work, Geoff was a pretty solid choice to voice match Robert, but his impression doesn't come out sounding that much like him during most of his lines. The way he says his name is basically perfect, but in other places, he seems to put on a very strange accent. He's okay, but he leaves something to be desired.