I've always found it curious not only that lower-case "g" has two rather distinct formal variants (as does lower-case "a") but that the variant generally found in serif fonts (and in many sans serif fonts) is quite possibly the most elaborate typographic form in the Roman alphabet. Take a look: the loop of the top part of the letterform extends from the top of the letter's x-height to between half and two-thirds of the way down to baseline (depending on typeface), after which a rather indecisive descender cuts left, veers right, then closes in on itself (or nearly so). Oh, and if that's not enough, the upper right portion of the top loop has grown an ear.
Unsurprisingly, even this particular variant form varies quite a bit from typeface to typeface. (My example is Bodoni.) The relation between the two loops, in size and relative position, the elaboration of the "ear," whether the lower loop is open or closed - all differ depending on typeface.
In some typefaces, the "double-story" lower-case "g" rather resembles a face in profile, with glasses and hair flowing back from the forehead and the mouth open. What is this character saying? It's obvious: "Yo, G."