Born to a Jewish family in New Rochelle, New York City,[4] Wellen was the son of Russian-born tailor, Hyman Levy, and a Russian American mother, Lillian Wilensky.

[1] In 1960, Wellen wrote a script for the ABC series Bourbon Street Beat entitled "Swamp Fire",[1] which aired on April 11,[10] directed by Andre de Toth.

[11] In 1964, first prize in Birmingham (Alabama) Festival of Arts television script competition went to Wellen's The Hubert Otis,[1] described by Variety as "a satire about a nobody with a yen to become a somebody by retaining a pubrelations firm.

[13] That same year, Wellen's novella Mind Slash Matter, about a screenwriter prematurely afflicted with Alzheimer's disease facing the added challenge of solving the murder for which he has just been framed, debuted in the Ed Gorman–Martin H. Greenberg anthology, Predators.

[14] In his 1995 collection, Tales of the Batman, Greenberg informed readers that Wellen's novella had been optioned by Tri-Star Pictures as a vehicle for Robin Williams.