On October 20, the original author of the Fernflower Java decompiler, Stiver, passed away after a long fight against glioblastoma.
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Twenty years ago, he developed a deep professional interest in Java virtual machine internals. You may remember his research blog posts, like this one (in Russian) from 2006 about how to tweak the Java class hierarchy using Unsafe when Java 1.5 was just released. Around 2008, Stiver became fascinated by Java decompilation.
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Stiver decided to write his own decompiler as a side project. To overcome the weaknesses of existing alternatives, he took a different approach. After reading the bytecode, he constructed a control-flow graph in static single-assignment form, which is much better to express the program semantics abstracting the particular shape of bytecode. At the beginning of this project, Stiver knew little about static analysis and compiler design and had to learn a lot, but the effort was worth it. The resulting decompiler produced much better results than anything available at that time. It could even decompile the bytecode produced by some obfuscators without any explicit support.
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Stiver did the main development himself between 2008 and 2010. The first public version became available in May 2009 as a web service. A user could upload an individual CLASS file or a whole JAR file and get the decompiled result. The decompiler quickly gained popularity – during the first four months, users decompiled more than half a million Java classes. There was no public standalone version, but Stiver sent it privately to a few Beta testers.
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In 2013, JetBrains approached Stiver with a suggestion to include Fernflower in IntelliJ IDEA. Part of the deal was making Fernflower open source. Everything went well, and the contract was signed. On July 11, 2014, the early access version of IntelliJ IDEA 14 was released, including the decompiler for the first time. You can still see the initial import of the Fernflower source code in the IntelliJ IDEA Git history, on March 4, 2014.
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As Fernflower became open source, many other tools in the Java world used it – you can find a number of forks on GitHub. The Java team at JetBrains is constantly improving Fernflower, but it’s still mainly Stiver’s code. 
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Thank you, Stiver! We are deeply saddened by the loss of such a brilliant pioneer whose work and dedication had such a lasting and profound impact.