When we pull down the font menu on our computer, we see the names of typefaces (or font families), each containing sets of individual letters that were designed to work together in any order. Some of these typefaces were designed hundreds of years ago, and some are relatively new, but if we look back over the grand scope of human history, the idea of typography itself is a pretty fresh concept. Until Johannes Gutenberg introduced movable type printing in the 15th century, the written word was just that: written.
The letterforms we see in fonts today can all, in some way, be traced back to handwriting. Knowing something about how a pen makes marks on paper can help explain why different typefaces look the way they do.
Before Gutenberg, documents and books were usually produced by scribes and scholars who wrote in one of three script styles: gothic, roman, or italic. Gothic is the oldest of these, typically found in religious manuscripts. Monks used a broad-nib pen to produce a tight, upright kind of writing. You may know it as "old english", but "blackletter" is a more appropriate term, and more descriptive of the dark, dense pages that resulted from the style.
While blackletter was still used in German-speaking texts well into the 1900s, much of the West rejected these scripts during the Italian Renaissance when lighter, more open forms were in fashion. The most carefully produced books were written in a style now known as "roman", which took its capital letters from classical stone inscriptions, while calligraphers favored the "italic" style whose narrow, space-efficient forms could be written more quickly. It wasn't until later in the 16th century that these separate styles were combined into type families, with a roman and italic of harmonious design.
As roman letters evolved, type designers gradually pushed the forms away from their handwritten origins. Typefaces became either more mechanical or more decorative. The strokes themselves became less calligraphic and more constructed. Serifs, the little marks at the ends of strokes, got more blocky, or more ornamental, or, as in the case of sans serifs, disappeared altogether.
The colorful variety of type we experience today is a result of that evolution, whether it's the regimented but graceful curves of Bodoni, the strict geometry of Futura, or the many script fonts that emulate formal calligraphy.