I started a thread to get some clearance about all the John/Jack (A./Joseph) Gallagher (Jr.) out there lately. This thread brought some results, but did not solve the main problem: Who is who?

Therefore I have to rely mostly on IMDB to split this monster thread to single common name finding threads...

Here is the thread for:

(J) John Gallagher Jr. (1984): Actor, Singer, Songwriter - aka. John Gallagher
Born June 17th, 1984 in Wilmington, Delaware
Known for: Short Term 12, Pieces of April, Jonah Hex, The Newsroom
Documentation: Wikipedia, IMDB as John Gallagher Jr.

The credits out of CLT:

John Gallagher:
• ETC: Experimental Television Center 1969-2009, Disc 3 - (J) John Gallagher Jr.

John Gallagher Jr:
• Jonah Hex - (J) John Gallagher Jr.

John Gallagher Jr.:
• The Good Student (Mr. Gibb) - (J) John Gallagher Jr. (person confirmed by Wikipedia) - credit confirmed by ateo357
• Jonah Hex - (J) John Gallagher Jr.
• Law & Order: Special Victims Unit: Year Ten - E15 - (J) John Gallagher Jr. - credit confirmed by AiAustria
• Margaret - (J) John Gallagher Jr. (person confirmed by Wikipedia) - credit confirmed by AiAustria
• The Newsroom: The Complete First Season - (J) John Gallagher Jr. (person confirmed by Wikipedia) - credit confirmed by greyghost
• The Newsroom: The Complete Second Season - (J) John Gallagher Jr. (person confirmed by Wikipedia) - credit confirmed by AiAustria
• Pieces of April - (J) John Gallagher Jr.
• Short Term 12 - (J) John Gallagher Jr. (person confirmed by Wikipedia)
• Si la cosa funciona (Whatever Works) - (J) John Gallagher Jr.
• The West Wing: The Complete Fourth Season - (J) John Gallagher Jr. (person confirmed by Wikipedia)

John Gallagher, Jr.:
• The Good Student - (J) John Gallagher Jr.
• Jonah Hex - (J) John Gallagher Jr. (person confirmed by Wikipedia) - credit confirmed by ateo357
• Law & Order: Criminal Intent The Third Year - (J) John Gallagher Jr.
• Law & Order: Special Victims Unit: Year Ten - (J) John Gallagher Jr.
• Margaret: Extended Cut - (J) John Gallagher Jr.
• The Newsroom - (J) John Gallagher Jr.
• The Newsroom: Segunda Temporada Completa (The Newsroom: The Second Complete Season) - (J) John Gallagher Jr.
• NYPD Blue: Season 11 - (J) John Gallagher Jr. (person confirmed by Wikipedia)
• Olive Kitteridge - (J) John Gallagher Jr. (person confirmed by Wikipedia)
• Pieces of April - (J) John Gallagher Jr. (person confirmed by Wikipedia) - credit confirmed by AiAustria
• The West Wing: The Complete Fourth Season: Disc 1 - (J) John Gallagher Jr. (person confirmed by Wikipedia) - credit confirmed by Scooter1836
• The West Wing: The Complete Series - (J) John Gallagher Jr.
• Whatever Works - (J) John Gallagher Jr. (person confirmed by Wikipedia) - credit confirmed by AiAustria

Per the rules the common name is John Gallagher, Jr..