[2] Samuel has been regarded as one of the best centre-backs of his generation,[3][4] and as one of football's toughest defenders,[5] with former international teammate and Inter captain Javier Zanetti referring to him as the "hardest player" he has played with.

He was born Walter Luján, making his professional debut for Newell's and playing the World Youth Cup under that name.

[13] In August 2005, he returned to the Serie A with a transfer to Inter Milan on a four-year contract for reported €16 million fee.

[14] He began his Inter adventure by winning the 2005 Supercoppa Italiana versus Juventus, entering in 63rd minute as Nerazzurri won at extra-time thanks to the winner of Verón.

[16] On 24 November, during a Champions League group stage match against Petržalka, Samuel played in a line-up of 11 foreign players on the pitch, with Luís Figo being the only european.

[17] He finished his first season at Inter by making 42 appearances in all competitions, with the team winning the championship following the relegation of Juventus due to match-fixing,[18] and Coppa Italia by defeating Roma 4–2 on aggregate, with Samuel playing on both finals,[19] thus completing an unforeseen domestic treble.

In the Derby della Madonnina on 23 December 2007, Samuel hurt himself whilst marking the Brazilian international Kaká, and a couple weeks later, he had reconstructive surgery on his anterior cruciate ligament.

[21] Samuel was one of the most important players under Mourinho in the 2009–10 season, partnering Lúcio in defence[22] as they won the Serie A title, the Coppa Italia, and the UEFA Champions League, completing a historic treble.

[23] He scored his first goal of the season on 20 October in the third Champions League group stage match versus Dynamo Kyiv which prevented Inter from losing;[24] he headed home a Wesley Sneijder cross to make it 2–2.

[24] Later on 9 January, Samuel scored a last-minute winner in the 4–3 win versus Siena by beating goalkeeper Gianluca Curci with a left-footed shot.

[citation needed] Samuel finished the season by making 42 appearances and scoring 4 goals; he was praised for his defensive performances against Barcelona and Bayern Munich on Inter's road to the Champions League title.

[39] Samuel wore the captain armband for the first time on 15 February 2014 in the 2–1 win at Fiorentina due to Javier Zanetti and Esteban Cambiasso being on bench.

[42] His last appearance for the club occurred on 10 May 2014 in the 4–1 home win over Lazio which gave the team a spot in UEFA Europa League next season.

[45] He played his domestic league debut for the club in the home game in the St. Jakob-Park on 31 August as Basel won 3–1 against Young Boys.

[11][56][57] At the end of the 2015–16 Super League season, under new head coach Urs Fischer, Samuel won the championship for the second time.

[68][citation needed] Regarded as one of the best defenders of his generation,[3] Samuel was a large, quick, powerful, and aggressive centre-back, who excelled in the air, both defensively, and as a goal threat on set pieces.

His defensive skills, which included an excellent positional sense, an ability to read the game, as well as tough, tight marking, and hard tackling, made him extremely effective at anticipating opponents.