Much has been written about the early history of MITS and the Altair. I will only briefly summarize it here.

The company was founded by Edward Roberts and 3 other fellow US Air Force acquaintances in 1969 in Albuquerque New Mexico, where they were stationed before they retired.  MITS stands for Micro Instrumentation and Telemetry Systems. They initially made radio control systems for model rockets. It was not a great success. Ed bought his partners out and refocused the company on selling kit electronic calculators. One was featured in Popular Electronics and initially it was a great success.   However when Texas Instruments got into the calculator business in the early 1970's the market collapsed.   Ed started to look around for something else to sell in kit form.
 

Quite unrelated but at the same time the editor of Popular Electronics (Les Solomon) was looking around for an article on a kit computer hobbyist could build for his magazine.  This was spurred on by an earlier article in the competing magazine Radio Electronics describing a primitive hobbyist computer (the Mark-8) utilizing an Intel 8008 CPU.  He contacted Ed who had written articles for him in the past about writing a computer kit for him.
 

The timing was right. Ed was playing around with the idea of making a computer kit utilizing an Intel 8080 CPU anyway.  He could get the CPU's at a discount for $75 each if he could sell in volume.  His goal was to have an 8 bit computer kit for hobbyist for less that $400.  The only problem was time. Solomon wanted the finished product for the January 1975 issue of Popular Electronics.  Ed and two of his staff worked non-stop to meet the deadline. They wanted to have a bus structure (as the Mark-8 had) so the kit could be expanded later with other components thereby increasing sales revenue.  In their scramble for low priced components they came across a deal on 100 pin connectors that seem to fit the need. The decided to layout their boards with 100 pin edge connectors.  In the rush unfortunately no great care or thought was given to optimum signal placements, ground lines etc.  Their computer had one front panel board, an 8080 CPU board and a 1K RAM board.  They called the computer the Altair.   As a side note, one of MITS cofounders Forrest Mims wrote the Altair documentation. He went on to be one or the most prolific authors in the computer industry.
 

After the write-up appeared in Popular Electronics demand for the kit exploded. They had budgeted to sell a few hundred kits. They sold 1000's in the first few months alone.
 

Ed refocused MITS to be  a micro-computer company.  His next project was to add more memory to the computer.  They designed, built and sold a 4K dynamic RAM card as an add-on to this "Altair bus". Unfortunately the design was faulty and did not work reliably.  Furthermore MITS was having problems  meeting the demand for its kits.  This allowed other companies such as IMSAI, NorthStar, Processor Technology etc. to get started and offer kit memory boards for the Altair. It was not long before they were making their own Altair like computers. 
 

Nevertheless the initial start gave MITS an early lead in the virgin market. In 1976 and 1977 the company grew rapidly. The company also had one other advantage, it was the computer Bill Gates utilized to developed his 4K Basic/Microsoft interpreter for.  Only later did Bill branch out and license his software to other manufactures. This was a time before floppy disks, where software was delivered via paper tape or possibly a cassette. Initially the main competition was IMSAI. The latter had better hardware implementations and definitely better marketeering.  MITS came out in 1977 with the Altair 8800b, an improved version of the Altair.  However the company got side tracked and jumped from the Intel 8080/Z80 CPU's to the Motorola 6800 chip that same year coming out with the Altair 680b.
 

Ed Roberts began to feel the company was growing too fast for him. He still remembered the growth and collapse of his calculator business and decided to sell MITS that year to Pertec, the disk drive manufacture (for $6.5M).  Ed dropped out of the computer business and went on to be a medical doctor -- something he always wanted to do.

With Pertec's help, MITS quickly implemented a disk drive interface for Altair's.  They also made the mistake initially of trying to force the use of their own disk operating system/software on users rather than the then popular CP/M system used by others.  By the end of the decade MITS and its S-100 bus products was gone. MITS just could not make the transition from a hobbyist driven business to a "normal" plug-and-play customer business that were often intimidated by the likes of led's, switches and cryptic instructions.