In the book The Prime of Miss Jean Brodie, the title character sometimes tells one of her students (I forget which one because I haven’t read the book in 20 years) that she is the leaven in the lump. This phrase came to mind because it is almost Passover and I have cleaned out anything leavened, anything that could potentially be leavened, etc.
I worked with a lovely lawyer once whose last name was Levin, and I sometimes thought of him as the Levin in the lump, although I certainly never told him that.
The last name “Levin” comes from the tribe of Levi, the Levite priests (Christian readers will recognize the term Leviticus).
“Leaven” must have something to do with lightness. “Luft” in German is air, as in the military term Luftwaffe and the sometimes affectionate term “luftmensch,” which means head-in-the-clouds-person and is actually Yiddish. Levitate and levity also denote/connote lightness. I love that levity is the opposite of gravity.