How could a paragon character be an antagonist?
I want to write a story featuring two main characters--Al and Bob.
In the beginning, Al, the paragon, will be a kind, friendly, competent and well-liked, whereas Bob, the protagonist, is unliked, vindictive and selfish.
The setting is, at least superficially, in a fantasy-fiction world, where a city-sized population resides an isolated, habitable zone amidst monster-infested wilderness (the specifics of these matters not; it suffices to imagine them sailing on shark-infested water in a city-sized ship)
There are also superheros in this community who are responsible for its defence and organization, to which both Al and Bob are new members early on.
Wanting to make Al a justifiable antagonist, I immediately thought of the following:
Al, seemingly good in every respect, is secretly scheming to exert dictatorial power over the community for his own enjoyment; rising to the occasion, Bob challenges Al's rule and defeats him.
I reject this plan, because the plot of seemingly good people seizing power only to reveal their selfish motive is simply too cliched and predictable, especially if the protagonist is at odds with said person.
More importantly, this seems to undermine the true-paragon nature of Al, invalidating the idea of a paragon-villain. since there was no paragon in the first place.
Al seizes power and bring about certain political revolution. For instance, he suggests the complete and permanent closure of the community from the outside world as a perfect defence mechanism, but this is against the ideals of some of the community's members, who want to eventually reclaim the outside world instead of hiding in such a protective cage forever. Bob champions the latter ideology, and brings the down-fall of Al, for better or for worse.
Concerns for this idea: somehow this plot also make Al seem like a genuine villain, with an ideology that most modern readers will likely disagree with. This could be a result of the poor choice of example-ideology above, or because it is simply not possible to imagine an indisputably paragon ideology to be assigned to an de-facto villain, at least for me.
Idea number three:
Al gathers influence and persuades, rather than coerce, the community at large to perform certain questionable plans, such as the one described above. Bob rises to challenge Al as the representative of a part of the community who disagree. They fight; Bob wins, and Al's plan is abandoned with public approval for the winner. Then, the community is immediately ravaged by a disaster that could have been prevented by Al's plan, showing that Al was right and Bob was wrong. Bob watches hopelessly as the people who gave him approval for oh-so-short a time contort in the clutches of death, and commits suicide in defeat.
So far, this is the most appealing of all ideas, the paragon was paragon from beginning to end, the ending is unpredictable and cathartic, and maybe a set-up for sequels if the suicide part is omitted.
I ask this question to see if there are existing examples of paragon characters being an antagonist and any criticism or suggestion to the idea(s).