Wren had already drawn up plans to rebuild St. Paul's Cathedral before the fire leveled the older, Gothic version. After the fire hit, he quickly increased his ambitions: nothing less than a complete plan for the rebuilding of the area devastated by the fire (seen above). Wren's plan is logical, grand, beautiful and, from a modern perspective, completely dull. It is doubtful that the baroque splendor of Wren's rebuilt St. Paul's (or the diverse beauty of the 50 other churches he rebuilt around the city) would stand out nearly so much at the heart of a network of equally baroque boulevards. Walking the streets around St. Paul's one is struck by the almost whimsical joy of catching a glimpse of this domed behemoth from a narrow side street, gradually weaving closer and closer until finally emerging onto a plaza with the sheer mass of the thing just there.
The inability of Wren or, even, King Charles II to navigate the dense and convoluted legal framework of property ownership in the old City is what we have to thank for unique and stunning sights such as a post-modern skyscraper rising up next to hundreds of year old churches on a street with a medieval footprint.
To put it differently: very successful architects almost always come with very healthy egos (an apocryphal story about Wren on his Wikipedia page recounts the following exchange with Charles II regarding the design of a royal building: "Charles II, who was over six feet tall, complained about the low ceilings. Wren, who was not so tall, replied that 'they were high enough,' at which the king crouched down until he was on a level with his Surveyor and strutted about saying, 'Ay, Ay, Sir Christopher, I think they are high enough.") The ego is understandable: how could you not have a massive ego if you designed St. Paul's Cathedral? It's necessary to think critically about this however: Wren wanted to rebuild London as a baroque city modeled largely on Bernini's projects in Rome. Of course he did. Sir Christopher was a baroque architect of genius, and this was how his city would look. But we can accept the vision of an architect of genius without totally wrapping our cities around that vision.
A case in point: Le Corbusier was one of, if not the, greatest architects of the 20th century. And he wanted the center of Paris to look like this: