Provide the names of competitors who received a gold medal.
names of competitors refer to full_name; gold medal refers to medal_name = 'Gold';
SELECT DISTINCT T1.full_name FROM person AS T1 INNER JOIN games_competitor AS T2 ON T1.id = T2.person_id INNER JOIN competitor_event AS T3 ON T2.id = T3.competitor_id INNER JOIN medal AS T4 ON T3.medal_id = T4.id WHERE T4.medal_name = 'Gold'