Sinclair Research Ltd. was founded in 1973 by Clive Sinclair (later: Sir Clive Sinclair) and was originally named 'Ablesdeal Ltd Inc.'. After some renaming, the MK14 ('microcomputer kit 14') was launched by Science of Cambridge Ltd., the ZX80 following shortly afterwards. Sinclair was then renamed to Sinclair Computers Ltd. and one year later, 1981, to Sinclair Research Limited. In the very same year the ZX81 was launched, which was in 1982 succeeded by the ZX Spectrum (aka ZX82). The Spectrum-series was Sinclair's breakthrough in the homecomputer-market and became their best-selling machine ever.
The demand for Sinclair's cheap and thus popular machines soon exceeded their production capacities, and so Sinclair began to cooperate with Timex Corporation, which already produced many of the ZX81s and Spectrums in Dundee, Scotland. Timex was allowed to build licensed clones of Sinclair's machines, mainly for the important US-market, so that Sinclair could concentrate on Europe. Most popular were the Timex Sinclair TS1000 (ZX81 clone with 2KB), the TS1500 (ZX81 clone with 16KB) and the TS2048 (Spectrum 16K clone).
Then, in January, 1984, Sinclair introduced the QL ('quantum leap' aka ZX83/ ZX84); it was no success at all, although it was one of the first 32 bit microcomputers (using Motorola's 'exotic' MC68008 CPU), with multitasking and high-res graphics, and Sinclair's first step into business markets. But as some say, it was released before completed, and so the owners of the early series machines were not very happy with it.
In 1985, after Timex Corp. had retreated from the US-market, Timex Portugal Lda. decided to sell Timex-machines in Portugal, Argentinia and Poland. In fact they did not only sell Sinclair-clones, but also developed their own, improved machines (like the TC2068 and TC2048).
Sinclair's end came in 1986, when AMSTRAD bought the rights on the Sinclair-logo and their homecomputer-series (although they continued to sell machines with Sinclair-brand for a while). From then on, Sinclair Research Ltd. was not longer allowed to produce computers, and Sir Sinclair concentrated on the other products they marketed. An interesting development lost in that process was the 'LoCC' ('low-cost Color Computer' a.k.a. 'Loki'), a Spectrum with 'Amiga-like capabilites'.
However, Sir Sinclair reported back to the computer market in the year of 1988, with the Z88. It was a cheap handheld computer with Z80 CPU and LC-display. Since Sinclair Research Ltd. was not allowed to build computers, he just founded another new company, 'Cambridge Computers', for selling the Z88. Nevertheless, many people call it the 'Sinclair ZX88'...

Today, it has become quiet around this pioneer in microcomputing technology... See the Sinclair Research Ltd. website for more info on what they do today.