Eric Olthwaite was, in 1934, considered to be the most boring man in Denley Moor, Yorkshire. His main interests were shovels and local rainfall statistics, while he was also captivated by how black a black pudding could be (his mother's black-puddings were sometimes so black that even the white bits were black).
Eric was so deeply detested by his family that his mother would find a task for him to do if he opened his mouth and spoke about an interesting topic, his sister was just downright rude, and his father pretended to be French to avoid talking to him. This ultimately became too much for the family to cope with, and they ran away from home one night (and even took the outside toilet).
In order to make himself more interesting, Eric decides to get a job at the bank. Alas, the bank manager (also played by Palin) tells him that he's too boring to work in the bank. It's at this point that Eric's fortunes change - the bank is robbed and he's taken hostage by Arthur (who wouldn't disclose his last name).
At gun point, a limousine containing the mayor is hijacked, during which the mayor recognises Eric ("Aren't you Jean Pierre Olthwaite's son?", soon followed with "Aye, you're the boring one!"). Pursued by the police, the entire escape scene is quite amusing, not least due to the chauffeur remaining thoroughly stiff and proper throughout.
After evading the police, Arthur is going to kill Eric (and kill him completely). His life is spared when Arthur realises that they share common interests (and Arthur also realises that he's seen Eric reading the rain gauge in Town Hall Square). They decide to form a gang, which they call "The Eric Olthwaite Gang".
A reign of terror ensues, during which shovels are stolen and rain gauges are distributed to the masses in a Robin Hood-like manner (only seen as newspaper headlines during the show). This makes Eric more famous than ever, even enticing his "girlfriend", who'd previously been more interested in having affairs with other men, to join the gang as their moll.
Eric's life of crime is eventually brought to an end when the bank manager and the mayor realise that their own lives are boring, and Eric is offered, and accepts, the mayorship of Denley Moor.
This is the moment that Eric becomes particularly interesting, with his parents and acquaintances reminiscing with fondness about Eric's boring interests (exposing the human folly of equating fame with being interesting).
The last view of Eric is during his inauguration speech, which the older townsfolk declare as interesting (despite the usual topics). The song that plays during the closing credits cites Eric as "The King of Denley Moor".