Ronaldus de Boer (; born 15 May 1970) is a Dutch former professional footballer who played as a midfielder. He played for the Netherlands national team as well as a host of professional clubs in Europe. He is the twin brother of Frank de Boer. The majority of his success as a football player was with Ajax. He works as the Ajax A1 assistant manager. Club career De Boer's first youth club was De Zouaven in Lutjebroek where he played before being selected for the Ajax youth programme in 1983. On the professional club level, De Boer played for Ajax (1988–91 and 1993–99), Twente (1991–93), Barcelona (1999–2000), Rangers (2000–04), Al-Rayyan (2004–05) and Al-Shamal (2005–08). In both Qatari clubs, he was reunited again with his brother Frank, his teammate at Ajax, Barcelona and Rangers. In his first spell at Ajax from 1988 to 1991, he won the Eredivisie title in 1989–90 under manager Leo Beenhakker. After two seasons at Twente from 1991 to 1993, he returned to Ajax under manager Louis van Gaal, and had his most successful spell as a player, winning three consecutive Eredivisie titles in 1993–94, 1994–95 and 1995–96. He also won the 1995 UEFA Champions League, the 1995 Intercontinental Cup, and the 1995 UEFA Super Cup. He was also a runner-up of the 1996 UEFA Champions League, where Ajax lost on penalties to Juventus. When Louis van Gaal left Ajax for Barcelona in July 1997, Morten Olsen became the new Ajax manager, and De Boer won a fifth Eredivisie title in 1997–98 and also won the 1997–98 KNVB Cup. There was then controversy soon after De Boer and his twin brother Frank signed a six-year contract extension with Ajax at the start 1998–99 season, when Ronald and Frank took successful legal action to have the contract voided. Ajax had agreed verbally that if a lucrative offer for one brother came by, he would be released provided the other stayed. Ajax, however, apparently backed down on that agreement after floating the club on the stock market and pledging to shareholders that it would hold both of the De Boers and build around them a team to recapture the UEFA Champions League. The fallout over the contract situation led to an increasing conflict between the De Boer twins and the Ajax hierarchy, with match results for Ajax suffering and manager Morten Olsen soon getting sacked. In January 1999, Frank