Apple first authorised the production and sale of clones in 1994 (with the first models reaching the market in 1995), but the first Mac clone was in fact produced almost 10 years earlier in Brazil.
As a consequence of the country's "reserved market policy", only computers produced by Brazilian companies were allowed to be sold in Brazil. PC clones were available but since the design of Macs was proprietary, it was impossible to purchase one legally in Brazil. A small company named Unitron wanted to rectify this situation. The initial plan was to negotiate some sort of licensing agreement with Apple. Unfortunately Apple refused to do this without owning at least 51% of the ensuing venture, which was prohibited under Brazilian law, so Unitron decided to go ahead without Apple's blessing. Unitron had already successfully cloned the Apple II without incurring Apple's wrath, so it seemed a realistic target.
Unitron's goal was to clone the Macintosh 512k (code-named Fat Mac). Many of the components were freely available, such as the MC68000 microprocessor, although this did not make obtaining them trivial, because of the restrictive import laws. A few however were custom designed, these included the IWM (floppy controller), the real time clock, and 4 PLAs. On the software side Unitron needed to produce copies of the Mac OS ROM which at the time contained most of the ToolBox.
Unitron was able to secure a loan from the government and eventually managed to reverse engineer the custom designed chips, with the help of various University laboratories and National Semiconductor. Unitron claimed that the ROM was rewritten based on specifications from the Inside Macintosh books. Written in a mixture of C and assembly, it was twice the size of the original ROM. Unitron was also able to translate the operating system (known simply as "System" in those days) into Portuguese.
In 1986 Unitron released the Mac512, the first Mac clone. Unsurprisingly Apple's curiosity was aroused and they managed to obtain a few of these machines. After disassembling them, Apple disputed the fact that the ROM had been reverse engineered. Apparently a few bytes had been changed to change the checksum, but the immense majority of the ROM had been copied. There is some dispute as to whether the machines that Apple obtained were merely prototypes fitted with copies of Apple ROMs for compatibility testing, whether it was only later models that had a reverse engineered ROM or whether Unitron never actually successfully reverse engineered the ROM at all.
Whatever the truth behind all of this was, it suffices to say that Apple was not happy with what they saw. It was not the so much the reverse engineering of the hardware which posed problem, but the alleged copying of the ROM. In 1987 They were able to persuade the American government to threaten Brazil with raising tariffs or lowering imports of key Brazilian products if Unitron did not cease the production of its clones. The Brazillian government was able to pressure Unitron into canning the project, and the designs were eventually sold to a Taiwanese company. Apple's lawyers descended on this company as well and so the story of the very first Mac clone ends.
In 1992, when the law changed and Apple was finally allowed to sell their computers in Brazil, virtually nobody had seen or heard of a Mac before. People had bought IBM clones because that was all that there was to buy. Had Apple not come down so hard on Unitron they could have established a foothold there. On the other hand, had the Unitron experiment been allowed to continue, the machines could have spread to other countries and eaten into Apple's profits. Even if it had not, it could have set a dangerous precedent for Apple.
Sources:
http://www2.uol.com.br/macpress/artigos/c028a00052.shtml
http://www.lsi.usp.br/~jecel/reserve.html
http://web.archive.org/web/20030620194342/http://www.applefritter.com/macclones/unitron/index.html
http://www.apple2.com.br/modules.php?name=Sections&op=viewarticle&artid=36
http://www.old-computers.com/museum/computer.asp?st=1&c=997
http://www.lsi.usp.br/~jecel/mac512.html
http://www.lowendmac.com/clones/unitron.html