"If you love Comic Sans, you don't know much about typography. If you hate it, you really don't know much about typography, either, and you should get another hobby."
-- Vincent Connare
Comic Sans is a popular font -- many would say too popular -- that was designed to be friendly and lighthearted in appearance, to be easy to read on a computer screen and non-assuming.
It was originally designed by Vincent Connare, a 'typographic engineer' at Microsoft (the same typographic engineer who designed Trebuchet). In 1994 Microsoft was putting together a project called Microsoft Bob, a cartoon house with cartoon characters that would help advise and organize users. Microsoft Bob was originally written in Times New Roman, which does not really go well with cartoonish interfaces. It looked cramped and stodgy, and Microsoft was willing to replace it if a suitable alternative could be found.
Mr. Connare was willing to take on the challenge, and decided to model his new font on the text found in comics -- he remembers that Batman: The Dark Knight Returns and Watchmen both helped influence him. Of course, these books were lettered by hand, meaning that each letter was slightly different, and that the text could be highly nuanced, with infinite variation in the darkness, size, shape, and mood of the text. The lettering also tended to be upper case. Comic Sans emerged as an idealized and simplified version of comic book text, with simple, clear lines, slightly off-kilter and with joins that are just barely imperfect. It looks like good, simple print handwriting, something that a very neat 12-year-old might write. As you might guess from the name, it is a sans serif font, and the lines, if you look closely, even have rounded ends.
Comic Sans gives text a cheerful, clean look. It is intended to be used for small text, at the standard 12-point font size. When blown up larger it begins to look more childlike, but this is not what it was designed for, and if you want child-like handwriting there are better fonts available. Sadly, Comic Sans never fulfilled its original destiny; the entire layout of Microsoft Bob was built around Times New Roman, and the slightly wider Comic Sans just didn't fit into the text boxes and speech balloons. It was, however, used in the later Microsoft Movie Maker, which ended up being a much more popular program.
Comic Sans became ridiculously popular when it was released to the general public, as a supplementary font in Windows 95. It was immediately recognized by the masses as a fun, informal font that was easy to read. Just the fact that it was designed for the computer screen put it well ahead of the cramped Times New Roman, which designed for narrow newspaper columns, and was packed tightly to save space and avoid disconcerting patterns in the white space between the letters. Unfortunately, too many people set Comic Sans as their default font, and it has wormed its way into nearly every inappropriate setting you can imagine; there are tales of it appearing in college essays and textbooks, of people being fired in Comic Sans e-mails, of it appearing on the side of ambulances, and of its finding its way onto at least one gravestone.
Over time, there has grown a surprisingly large and sometimes dour movement against Comic Sans. I shall not dwell on this movement, but if you would like to learn more, the Ban Comic Sans website is still up and running strong after a decade of good-natured grouchiness. I say that while it is important to recognize that your choice of a font does influence what people think of you, and that Comic Sans is widely disapproved of, it is also important to remember that sometimes it's okay to talk like Batman.