I was told aqualung was named after a homeless person I used to see back in the late 1970s in Charleston WV.
Here's what I found at The Official Jethro Tull Website
QuickfactsAqualung (song) - WikipediaThe first two verses of "Aqualung" were cowritten with Anderson's first wife.
"Hymn 43" became the first Tull single released in the U.S.
"Aqualung," the song, got its name from the gurgling sound of underwater diving gear which Anderson felt described the wheezing of the song's character. Anderson did not know that "Aqualung" was a trademark and not a generic phrase (the issue was settled quite amicably).
The cover, with "Aqualung" bearing an all too close likeness of Anderson, is one of Ian's least favorites. Yet, it set a precedent for future Tull characters being pictured as "Ian-like" including Ray Lomas from "Too Old to Rock and Roll" and the covers of "Songs from the Wood" and "Stormwatch."
In an interview with Ian Anderson in the September 1999 Guitar World interview he says:Aqualung wasn't a concept album, although a lot of people thought so. The idea came about from a photograph my wife at the time took of a tramp in London. I had feelings of guilt about the homeless, as well as fear and insecurity with people like that who seem a little scary. And I suppose all of that was combined with a slightly romanticized picture of the person who is homeless but yet a free spirit, who either won't or can't join in society's prescribed formats.
So from that photograph and those sentiments, I began writing the words to 'Aqualung.' I can remember sitting in a hotel room in L.A., working out the chord structure for the verses. It's quite a tortured tangle of chords, but it was meant to really drag you here and there and then set you down into the more gentle acoustic section of the song.[2]