Why do we call First Sergeants "1st Shirt"?

Nobody ever called me Top or First Shirt twice in my company.  I was the First Sergeant and would be addressed as that. I didn't address my seniors as SMADGE.  It is about respect.

I found this in an Air Force magazine. Seems nobody knows for sure, but they offered three theories, which all seem to go back to pre-Air Force (i.e. Army) days, though strangely enough, I've never heard of this term in the Army itself. Anyway, here are the theories:<div><br></div><div><p style="color: rgb(0, 0, 0); font-family: Helvetica, Arial, Verdana, sans-serif;">The first and most colorful version has it that federal troops in the early frontier days wore their shirts into tatters and eagerly awaited the supply wagon bringing new uniforms. When it came, the first sergeant, being the ranking enlisted man, got the first pick of the shirts.</p><p style="color: rgb(0, 0, 0); font-family: Helvetica, Arial, Verdana, sans-serif;"><br></p><p style="color: rgb(0, 0, 0); font-family: Helvetica, Arial, Verdana, sans-serif;">The second theory is that the first sergeant, being the most senior and usually the most experienced of soldiers, often collected more decorations and insignia than anyone else. His shirt thus was the gaudiest—the first—in the outfit.</p><p style="color: rgb(0, 0, 0); font-family: Helvetica, Arial, Verdana, sans-serif;"><br></p><p style="color: rgb(0, 0, 0); font-family: Helvetica, Arial, Verdana, sans-serif;">The third explanation is that when the Army troops removed their shirts to work in hot weather, the first sergeant continued to wear his because he was boss of the work crew and did not do manual labor. When anyone wanted instruction on some subject, he was told to see “the shirt.”</p></div>

When I was in the service we called him "TOP" or First Sergeant. I think it depended