Its source is Helen, an English name meaning "Sun ray."
The dropping and adding of the initial letter ''h'' in Ellen and Helen probably reflects shifts in pronunciation over time and geography, and perhaps over socio-economic lines as well.
G.B. Shaw's 1913 play Pygmalion turns on the pronunciation of the phrase ''In Hartford, Hereford and Hampshire, hurricanes hardly ever happen.'' Ambitious Cockney flower girl Eliza Doolittle struggles for much of the play to pronounce the ''h's'' and refrain from inserting one at the beginning of the word ''ever.'' She knows adopting the pronunciation favored by the upper classes could help her realize her ambition of selling flowers in a shop, rather than hawking them on the streets of London.
Other name pairs with ''h'' and ''h-less'' versions include Eloise and Heloise, and Ester and Hester.