No profession is free from the kind of miserable jerks who ruin it for everyone else. No intelligence level is either. When great intelligence, prestige careers, and big egos come together, things get ugly. Johann Bernoulli was, as a person, very ugly.
Johann and Jakob
The Bernoullis were a 15o-year dynasty of brilliant mathematicians and physicists who, from 1654 to 1807, worked on everything from probability to fluid dynamics. Johann was the younger brother of the now-more-popular Jakob Bernoulli, who worked out how likely it was that a coin with a 50% probability of landing heads or tails would actually show those 50/50 odds during a given run. This involved a massive amount of work, and Jakob died while he was still compiling a table of odds.
People went to Johann trying to get him to complete his older brother's work. Not only was Johann a gifted mathematician, he owed quite a bit to Jakob, as Jakob was his math teacher while they were growing up. Johann still said no. And that was probably the nicest encounter anyone ever had with him.
The Mean Game of Math
To be fair, mathematics wasn't a very nice profession at the time. Johann believed that he had previously been screwed over by his student. Guillame L'Hopital took Johann's lecture notes, which included an important proof, and published it himself, even crediting himself with the proof and calling it L'Hopital's rule, or so Johann claimed.
Johann made no effort whatsoever to raise the bar of courtesy and kindness in his profession, but his targets were often members of his own family. His rivalry with Jakob began when Jakob started corresponding with Gottfriend Leibniz, who the brothers both idolized, but kept Johann out of the conversation. During the correspondence, Jakob came up with the calculus term "integral," which Johann subsequently claimed was his. Johann responded to Jakob's publication by publishing the solution to a problem and crowing that his brother couldn't solve it. Jakob, Johann claimed, then started adding bits to Johann's papers before publication. The rivalry turned more and more bitter over the years, mostly in major mathematics publications.
Who Was At Fault?
How much is Johann responsible for the estrangement? We can only guess, but those guesses don't have to be a wild stab in the dark. Johann had a son, Daniel, who grew up to be as talented as his father. This was a major problem for his father. Daniel won a mathematics prize, which Johann had also been in the running for it. Johann got his own son kicked out of the Academy of Sciences. When Daniel published a book on hydrodynamics, Johann copied it, except for the publication date. He backdated it, making it look like he had actually published first.
In the end, it seems that Johann might have gotten quite a bit more done if he'd spent less time trying to make it look like he'd gotten a lot done. It might also have been better for him if he'd been in a less talented family. No one would want Johann for a father, but was he the world's meanest scientist? You decide.