when did he change his name? Article in Shropshire Star implies that this happened between 1940 (when he started working at the Wolverhampton Repertory Company) and 1942 (when he joined the Army).
parents: I don't have cast-iron proof yet but I believe his parents were Oscar Max Ohm (11 Aug 1890, Wem, Shropshire - 17 Feb 1968, Shrewsbury, Shropshire) and Marion Evelina (Eva) Wright (9 Dec 1897 where? - 23 Oct 1972, Shropshire). Many biographies state that Max was Austrian but I think this is a misunderstanding - Max's grandfather Gothard was born in Prussia, which included Austria, but later generations were English.
"England and Wales Marriage Registration Index, 1837-2005," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:QVDX-CTZB : 8 October 2014), Peter E Ohm and null, 1952; from “England & Wales Marriages, 1837-2005,” database, findmypast (http://www.findmypast.com : 2012); citing 1952, quarter 4, vol. 5C, p. 2092, Kensington, London, England, General Register Office, Southport, England.