Firstly, I must apologize for being unable to put into context exactly why I adore this number above all others. To explain very briefly, I would say it's properties are simply unbelievable. Also known as Phi, or the Golden Ratio, it has an uncanny way of appearing in the strangest places. .
To put it simply, an object or image that has the dimensions of Phi is said to have the most visually appealing dimensions. An example would be the Golden Rectangle, (which is the only rectangle that can form into itself in a mollusk-shell shape until infinity - see below in Fibonacci Numbers section) or the Golden Section. (a line cut at "an extreme and mean ratio" - see below) Note how these simple shapes (i.e. the mollusk- shell,) appear most frequently in nature - snail shells, and even apple-seed stars that form a pentagram, have proportions to Phi.
Geometric shapes of these (Golden Ratio) dimensions can also be found in magnificent works of art - and most mathematicians agree, they are magnificent because of their dimensions! Even in the human body, the closer your body's dimensions are to the Golden Ratio, the more beautiful you are. For example, if the ratio of the length from your feet to your navel, and from your navel to the top of your head is equal to Phi, you have the ideally proportioned height! Theories of this sort have just started to come out, (in the 21st century!) and are being used in corrective surgery. .
Plato (428/427 B.C. - 348/347 B.C.) saw these geometric shapes of the Golden Ratio, (also known as the Platonic Solids) as universal shapes of extreme importance. I personally agree.
For more information on this incredible number, see The Golden Ratio by Mario Livio. .