|Born|| March 14, 1992 |
|Height||6 ft 0.5 in (1.84 m)|
|Weight||203 lb (92 kg; 14 st 7 lb)|
| NHL team|
| Chicago Blackhawks|
|NHL Draft|| 93rd overall, 2012|
Erik began playing hockey in Nynäshamns IF before moving to Djurgården's youth organisation. Gustafsson represented team Stockholm in the 2008 TV-pucken, a national junior tournament, scoring four assists. He played the 2008–09 season with Djurgården's under-18 team.
In the following season, Erik played for both the under-18 team and the J20-team.
For the 2010–11 season, Erik had a permanent place in the J20-team which won their division and ended up third in the playoffs. In May of 2011, he extended his contract with Djurgården through the 2013–14 season.
Erik was called to make his Elitserien debut in the league premier against HV71 on September 15, 2011, but he did not receive any time on the ice.
In Erik's second game against Brynäs on September 27, 2011, he made his on-ice debut, playing six minutes of the game. He scored his first Elitserien goal on December 26, 2011 against Fredrik Norrena of Linköpings HC.
On April 4, 2013 (with Djurgården remaining in the Allsvenskan), he left to return to the top level SHL in signing a contract with Frölunda HC.
After two successful seasons establishing himself in the SHL with Frölunda and with his NHL rights from Edmonton not retained, Erik signed a two-year contract with the Chicago Blackhawks on April 30, 2015.
Erik has two brothers: an older brother, Joakim (born on February 25, 1989) and a younger brother Glenn (born on September 4, 1998) who also play hockey in Sweden.