- 古伦木! - 欧巴! Meaning in this context?
古伦木 and 欧巴 are not character names but two lines in 奇袭白虎团, which is a Korean-war-themed 'Modern Peking Opera'（革命现代京剧, Peking operas written in PRC）. The plot involving this two lines is (which is historically accurate, based on records in the Korean War): the Chinese army and North Korean army learn from a South Korean captive the password of a certain South Korean checkpoint and successfully pass this checkpoint using the password. The password is &quot;A: 古轮木 B: 欧巴&quot;. (It is said that 古轮木 is from Korean 구름 gureum [cloud] and 欧巴 from 우박 ubak [hail].)
The movie In the Heat of the Sun focused on youngsters who grew up in the Cultural Revolution era. Eight selected modern Peking operas, or 八大样板戏 Eight Model Operas, are the most-often performed and the most influential operas during that time. Almost everyone then knows these two lines. In the movie, Ma Xiaojun and his gang use these to tease the fool 傻子, who always answers with 欧巴 when asked with 古轮木 (an imitation of that opera). However in the end of the movie, when they, as grown-ups, meet the fool and try to tease him again, the fool answers with 傻屄 stupid cunt. It represents the end of dissipated youth of Ma Xiaojun.
Jiang Wen used this as a symbol of the Cultural Revolution era and his youth (he has grown up in the same era and the same environment as Ma Xiaojun, and the movie can be seen as his attempt to put his youth memories onto the screen).
Jiang Wen's movies are not easy to understand (the meaning of the character of the fool is still often discussed in China today), let alone to people with little knowledge of that special era (including today's Chinese young men who were born after the Cultural Revolution and didn't experience it personally).
The full text of 奇袭白虎团 can be found here: http://www.mzdbl.com.cn/yinyue/gepian/baihutuan.html
The discussion of the character 傻子 on Zhihu:
https://www.zhihu.com/question/30430096