From the indispensable blog of Jess Nevins:
Still another Gopher of distinction was Happy Jack Mulraney, so called because he always appeared to be laughing. However, his smile was caused by a partial paralysis of the muscles of his face. In reality Happy Jack was a verjuiced person and very sensitive about his deformity; when his chieftains wished to enrage him against an enemy they told him that slighting remarks had been made about his permanent grin. Happy Jack was finally sent to prison for the murder of Paddy the Priest, who owned a saloon in Tenth avenue and was a staunch friend of Happy Jack’s until he asked the gangster why he did not laugh on the other side of his face. Happy Jack then shot him and for good measure robbed the till.