1 n. — Hockey
Wayne Gretzky's popularization of hockey in California and other US states.
Type: 4. Culturally Significant — Gretzky's trade from the Edmonton Oilers to the LA Kings in 1988 was a significant event in both Canadian and American sports history. Many Canadians were upset and felt Gretzky's departure also meant a more general departure of hockey from Canada (see CBC reference), and this opinion is still prevalent 25 years later (see the 2013 quotation). Gretzky's trade to the LA Kings, however, immediately popularized hockey in California among residents and the local celebrities alike, and eventually led to the expansion of the NHL into other cities in California (Anaheim and San Jose) and into other US states. Gretzky's presence also encouraged youth in California to take up hockey themselves, which has expanded the sport's talent pool (see the 2010 quotation). As Chart 1 shows, the term is nearly exclusive to Canada.
See also: The Great One
2 n. — Hockey
Wayne Gretzky's effect on his teammates, making them better players overall.
Type: 4. Culturally Significant — Gretzky's natural leadership, sportsmanship, and abilities positively affected his teammates' playing (see the 2009 quotation).
See also: The Great One
3 n. — now rare
brain drain; a movement of talent (both hockey and otherwise) from Canada to the US.
Type: 4. Culturally Significant — Early meanings of the term refer to the meaning of skilled hockey players, starting most significantly with Wayne Gretzky, leaving Canadian teams to play for American ones. The Gretzky effect was adopted as a term by some in the social sciences (see the 1989 quotation), but this meaning seems to have been superseded by meaning 1 above.
See also: The Great One
Images:

Chart 1: Internet Domain Search, 13 Aug. 2013