Rayon  (which is commonly known as Viscose),  was made  to substitute for the expensive silk.First manufacturer  is an American Company  Avtex Fibers Inc.  They made first production in 1910.
Different kinds of rayons exists , and most of them are highly absorbent, easy to dye, soft on the skin  and became very popular when it was first produced.
Viscose material is softer than cotton and more springy than silk. Viscose is comfortable to wear
Natural and artificial fibers ; Natural fibers are cotton, wool and silk and artificial are synthesized with petrochemicals like nylon and polyester. Even it is considered to be synthetic, it is not,  it is made from tree cellulose.

Difference between Rayon and Viscose ?  (and others)
The environmental profiles of rayon or viscose and they different. The Fibres are not named for its raw-material, but for its process.This  is confusing  many people.

Yarn producing that is the basis for rayon or vicose, raw-material generally from wood pulp, has to go through a chemical process. The process is much like how one produces paper. Depending on what type of process, the rayon can end up as Rayon, Viscose , Modal , Lyocell or Bamboo.

What is Cellulose : It is an organic compound and the structural component of most green plants. It is composed of the three elements: carbon, hydrogen, and oxygen. In general, its chemical formula is C6H6O5. For example, cotton contains 82.7% of cellulose, ramie - 68.6%, hemp - 67%.
What is Rayon :  Rayon is produced from naturally occurring polymers, and is called an artificial silk. It is not a synthetic fiber, but a manufactured regenerated cellulosic fiber. Rayon is very versatile and has the same comfort properties as other natural fibers: it can imitate the feel and texture of silk, wool, cotton and linen. Rayon fabrics are soft, smooth, cool, comfortable, and highly absorbent, but they do not insulate body heat making them ideal for use in hot and humid climates.
What is Viscose: Georges Audemars developed the first rayon fibre around 1855, but his method was impractical for commercial use. Hilaire de Charbonnet, Comte de Chardonnay, patented "Chardonnay silk" in 1884, but it was so flammable it had no safe use. Finally, in 1894, Charles Frederick Cross, Edward John Bevan, and Clayton Beadle patented the first safe and practical artificial silk, which they named "viscose". Avtex Fibers Incorporated began selling their formulation in 1910 in the United States.

Thanks To Sources: KMK MODA LTD, Mr. Kaan Karahan Interview ,Wikipedia.org., Mindfully.org ,MadeHow.com,imrsheep.com, www.whatisviscose.com