John Patrick O'Neill (born 11 March 1958) is a former footballer who played for the Northern Ireland national team, winning 39 caps, and scoring two goals.
 Born in Derry, Northern Ireland, he was a member of the Northern Ireland squads that played in the World Cup tournaments of 1982 and 1986.
 His final appearance for the national side came in their 3-0 defeat against Brazil in the 1986 tournament.
Andrew William Smith (born 25 September 1980) is a former Northern Ireland international footballer.
 He had a 16-year career playing professional and semi-professional football in Northern Ireland, England, Scotland, Belgium, and Portugal.
 He also won 18 caps for Northern Ireland between 2003 and 2005 and one cap for the Northern Ireland B team in 2003.
Anthony "Tony" Marchi (born 21 January 1933 in Edmonton) is an English retired football player of Italian descent, who played for Tottenham Hotspur in the position of wing half from 1950 until 1965, which was broken up by a two-year spell in Italy with Vicenza and Torino.
 During much of his career at Spurs, Marchi was mostly used as an understudy to Danny Blanchflower and Dave Mackay.
 However, in the 1962-63 following injuries he established himself in the side and was a member of the 1963 UEFA Cup Winners' Cup Final winning team.
 He was one of seventeen players used by Spurs in their Double winning side of 1960-61 He also later managed Cambridge City and Northampton Town.
David Healy is a retired association footballer, who represented the Northern Ireland national football team between 2000 and 2013.
 During his international career, he played 95 matches in which he scored 36 goals, becoming his country's top scorer.
 Healy made his international debut in a friendly against Luxembourg at the Stade Josy Barthel in February 2000, scoring two goals in a 3–1 victory.
 In June 2004, he became Northern Ireland's all-time top scorer, after netting his 14th international goal in a friendly against Trinidad and Tobago; the previous record of 13 goals was held jointly by Billy Gillespie and Colin Clarke.
 As of October 2015, Kyle Lafferty is second to Healy in Northern Ireland's all-time scoring record, with 16 goals.
 Healy's final goal came in 2012, after a four-year goal drought, when he scored a 95th-minute equaliser against Azerbaijan during the 2014 FIFA World Cup qualification.
Alan McDonald (12 October 1963 – 23 June 2012) was a Northern Ireland footballer and manager.
 As a player, he spent most of his career in England with Queens Park Rangers, as well as having short spells with Charlton Athletic and Swindon Town.
 He was capped 52 times for Northern Ireland and played at the 1986 FIFA World Cup in Mexico.
 After retiring as a player, he managed IFA Premiership side Glentoran from June 2007 until his resignation at the end of February 2010.
 McDonald collapsed and died whilst playing golf at the Temple Golf Club near Lisburn on 23 June 2012.
Brendan Duddy (10 June 1936 – 12 May 2017) was a businessman from Derry, Northern Ireland, who played a key role in the Northern Ireland peace process.
 A notable Catholic republican, who was a pacifist and firm believer in dialogue, Duddy became known by MI6 as "The Contact."
 In his book "Great Hatred; Little Room – Making Peace in Northern Ireland", Tony Blair's political advisor Jonathan Powell described Duddy as the "key" which led to discussions between republicans and MI6, and ultimately the Northern Ireland peace process.
Richard Stephen Graham (born 5 August 1979) is a retired Northern Ireland footballer who is assistant manager for Wingate & Finchley.
 He played as a left-midfielder.
Robert Dennis "Danny" Blanchflower (10 February 1926 – 9 December 1993) was a former Northern Ireland international footballer and football manager, and journalist who captained Tottenham Hotspur during its double-winning season of 1960–61.
 He was ranked as the greatest player in Spurs history by "The Times" in 2009.
 He played as a right half and was known for his accurate passing and ability to dictate the tempo of the game.
Paul Christopher Ramsey (born 3 September 1962 in Derry, Northern Ireland) is a former professional footballer and Northern Ireland international who played in a defensive midfield role.
 He featured for Northern Ireland in the 1986 FIFA World Cup.
Samuel Nelson (born 1 April 1949 in Belfast, Northern Ireland) is a Northern Ireland former footballer, who played for Arsenal, Brighton & Hove Albion and Northern Ireland throughout his career.

Question: What Northern Ireland footballer was Tony Marchi an understudy to?
Answer: Danny Blanchflower