I wish there was more to say about this, but there's not a lot written as a matter of public record in Charles Dickens' biographies. Suffice to say that I think fate is a curious thing, because some people experience power early on and other people find it elusive their whole lives. Doesn't it seem sometimes like precocious kids always get it easier and have it in for the geezers?
The story goes like this. In 1836, there was an illustrator by the name of Robert Seymour who gave up a career as a draughtsman to do sport caricature illustrations in the style of the famous George Cruikshank. Apparently, Seymour thought so much of Cruikshank that he liked to refer to himself as "Short Shanks" as a pseudonym. I never really cared too much for Cruikshank style, because the faces are always so poorly done, but to each his own. It was the popular style back then.
The publishers Chapman and Hall really liked what Seymour was doing and wanted to offer him a chance to work with a new writer that was becoming ridiculously famous, the 23 year-old Charles Dickens. The contract was that Seymour would do some etchings around the idea "The Adventures of the Nimrod Club" and Dickens would be approached to write some short stories based on them, but the focus would be primarily on Seymour. The illustrator would be the top billing.

"Better Luck Next Time" by Robert Seymour.
Dickens, however, was cocky and rather full of himself at the time, so he went to the top brass at Chapman and Hall and convinced them that his popular "sketches" stories should be the focus (what would become the The Pickwick Papers) and Seymour should get second billing as the illustrator. Dickens had only recently published his first book, Sketches by Boz - illustrated by Cruikshank (no less), and was transitioning himself from being a reporter to writing stories full time. Seymour had been working equally hard to get a good deal with Chapman and Hall for years and then Dickens somehow spoiled it for him.
Seymour, it is said, was very depressive and self-conscious throughout his life. He was arguably at least twelve years Dicken's senior and had never really caught this sort of lucky coup or popularity that young Dickens experienced. The publishers fawned over Dickens' ideas. To make matters worse, Dickens didn't seem to like either Seymour or his etchings. Coming back from his honeymoon (he married Catherine Hogarth on April 2nd), Dickens opined that Seymour had drawn Mr. Pickwick all wrong. The character was supposed to be fat, not thin. A meeting was set up in early April by Dickens at a local inn so that he could talk to Seymour and some of the publishing staff about the next installment to be published. I'm guessing Dickens related what it was like working with Cruikshank previously. We do know that Seymour ended the meeting by storming out. Seymour's ideas for the story were consistently being pushed aside.
On April 20th, after just 6 etchings with Dickens, Seymour received another letter of "commentary" by Dickens about what needed to be included in the next illustration. Seymour responded by promptly going out back to the shack in his garden and blowing his brains out with a shotgun. The publication didn't take a break until a month later, when Dicken's sister-in-law passed away from illness. Dickens replaced Seymour with Hablot Knight Browne, who was 21 and did a better Cruikshank imitation. Browne referred to himself frequently as "N.E.M.O." as in "no man," which is either self-derogatory or means that Browne liked his anonymity. Either way, Dickens liked his contemporary Browne enough to dub him Phiz. As Boz and Phiz, they worked together for many years. And this is what history remembers.
"No other illustrator ever created the true Dickens characters with the precise and correct quantum of exaggeration. No other illustrator ever breathed the true Dickens atmosphere, in which clerks are clerks and yet at the same time elves."
- G.K. Chesterton on H.K. Browne
