Obstructive Zealot

When people zealously pursue some higher goal, they tend to see only what they want to see, make bad choices, and alienate others. Well, this character knows the truth, understands the situation, and is in complete control... in his own mind, anyway. The truth is, he's entirely insane or an idiot. At best, he's tragically misinformed and will lead our heroes to near-disaster with his relentless interference, refusal to listen, and rejection of anything and everything that doesn't jibe with the Truth that he knows. This character often (but not always) shares characteristics with the Obstructive Bureaucrat, the Heteronormative Crusader and the Inspector Javert. Sometimes a member of an Animal Wrongs Group.

Examples of Obstructive Zealot include:

Cornelius Fudge, Minister for Magic in the Harry Potter series.
Special Agent Dammers from The Frighteners
Miko Miyazaki from The Order of the Stick, more so over time.
Dale from King of the Hill is a humourous example.
Cavaldi from The Brothers Grimm
The Masters (formerly The Bloodguard) in The Last Chronicles of Thomas Covenant are an entire race of Obstructive Zealots. They've set themselves up as the rulers of The Land - denying the people of The Land proper knowledge of Earthpower for starters - all for the purposes of being the only ones capable of defeating Lord Foul. Though it's obvious to anyone not one of The Masters that they don't have the numbers to wage war against Foul, let alone win.
Judicator Aldaris in StarCraft. He is willing to engage in a civil war while his home planet is being invaded by the nigh-unstoppable Zerg just because he doesn't like the people that the player and Tassadar are consorting with. Naturally, this blows up in his face and he accepts the truth. What makes it kinda tragic is that the next time Aldaris started to become an Obstructive Zealot, he was 100% correct. He could see that Kerrigan had gained some influence over the Matriarch, but nobody would listen to him (except his loyal core of off-screen supporters). And then Kerrigan shows up to kill him off before he could explain his reasoning for starting another civil conflict.
Yevonites in Final Fantasy X; they'll irritate you with scripture, feed you lies, and take issue with a certain member of your party. That's all before they brand The Hero a heretic and try to kill you. Doesn't help that one member of your party is a pretty strict Yevonite. D'oh.
Reverend Darren England, of the Whateley Universe. He's fought demons and aliens for decades, protecting the people of earth. Now he's trying to destroy a couple more inhuman things. They just happen to be some of the heroes.
Count Veger, with emphasis on the zealot. And "emphasis on the zealot" means "inscribe ZEALOT on him in ten-foot letters made out of solid gold".
Qing-jao (sp?) of Xenocide. She's seen as a brilliant individual who's easily the pinnacle of everything her home world of Path is about. Naturally, she's the one put in charge of a formal investigation into Demosthenes' identity, and actually winds up learning a great deal. But then it's revealed that the "godspoken" of her home world that ultimately guide everything are in fact genetically altered by humanity's governing body to act as hyperintelligent servants to fight against Demosthenes and anyone else that would dare to undermine them so thoroughly. The gods talking to them and their pathological obsessions to engage in demanding, menial activities are actually the results of genetically enforced OCD that keep them under control and unable to resist the call of their superiors. When Qing-jao is confronted with the truth, she defies it constantly, and even when it's cured in the end, she still insists the "gods" have a plan for her, and refuses to listen to any reason except her own. This troper was strongly reminded of Qing-jao when Miko Miyazaki finally fell.
The traditionalists in the church choir in All the Small Things are utterly opposed to the reforms introduced to the church by the new curate.
Donald Morgan of The Dresden Files, who firmly believes that Harry is a walking Black Magic time bomb who should have been executed years ago. Any attempts on Harry's part to defend himself are generally ignored. He eventually backs down a little from his Inspector Javert attitude, but he's still an obstructive jerk.
Commissar Tomas Beije in The Traitor's Hand, whom Ciaphas Cain makes the mistake of purposefully annoying because he expects not to have much dealings with him. Religious, zealous, and plain dumb, he sees Cain as a complete scoundrel, which ironically enough from the point of view of Cain's own narration is something of a Cassandra Truth. Of course, when he finally starts getting properly obstructive, it's just when Cain is trying to save everyone (even if it is because that includes himself). Although his attempts to get Cain punished backfire spectacularly thank to a combination of the fact Cain is HERO OF THE IMPERIUM, was engaged in the aformentioned day-saving and is friends with the Lord General. The tribunal's verdict boiled down to; "Commissar Cain is aquitted of all charges. Commissar Beije is now charged with getting in his damn way!".
Knight Commander Meredith in the Templar path of Dragon Age II. Meredith is so paranoid and delusional that she believes that Hawke somehow orchestrated the entire Mage-Templar conflict even after Hawke helped her destroy the Kirkwall Circle. Meredith is convinced that she is the Big Good and Hawke is the Big Bad when it's really the other way around.