A number of years ago, Ross supervised the experiments of David Banner, who was trying to improve humanity via genetics. However, Ross decided to shut down Banner's research when he found out that the scientist was making dangerous experiments on himself without the government's approval. In a rage, Banner made the whole base explode, forcing Ross and his men to leave.
Years later, Ross has become a general, and he has had a daughter, Betty, who hates him. After many years of silence between the two of them, Thunderbolt Ross contacts his daughter, since he's worried about David's son, Bruce's research. The son, in fact, is starting to work in the same field of his father, and Ross is concerned about it. Betty, anyway, doesn't want to listen to him and leaves, enraged and disappointed.
After Bruce's first transformation into the Hulk, Ross puts Banner under house arrest for security, preventing him from entering his lab. However, after being provoked by both his father and Glenn Talbot, Bruce transforms again and breaks free, injuring several soldiers in the process, so Ross decides to take him into an underground base, in which he keeps him prisoner, for both his and others' security. Betty tries to convince her father that she can help Bruce in controlling the Hulk, but Ross, out of arrogance, blindly believes that he is the same as his father, and does not agree. Later, it is revealed he doesn't have a choice in the matter to let her see Bruce anyway since Talbot has convinced the NSA to give him effective control of Bruce.
Meanwhile, Talbot tries to steal a fragment of Hulk's skin to make research on it, but he only manages to free the brute in the base, which cannot in any way contain it. When the Hulk breaks free, Thunderbolt Ross regains control and leads the military to hunt him down, having secured a National Command Authority Override from the President. But the monster destroys 4 tanks and 2 helicopters, later fleeing to San Francisco. In here, he's calmed down by Betty and the Army can take him in custody once again.
Because of an agreement between Betty and David Banner, the latter is allowed to speak with his son, despite the General's disagreement. After witnessing Bruce counter his own father on the monitor, Ross slowly begins to realize how wrong he was about him. David eventually bites a large cable connected to an incinerator aimed at him and Bruce, so Ross orders one of his men to turn on the machine and kill them both so the situation doesn't get out of hand. This has the opposite effect and David absorbs all the electricity in San Fransisco and David and the Hulk start a massive fight at Pear Lake. Ross watches them and then orders two fighter jets to fire a Gamma Charge Bomb at David's massive energy bubble form, aiding Bruce by putting an end to the battle and causing David to explode.
In the aftermath, Ross thinks Bruce had also died in the explosion and starts regretting his actions towards him. Betty comforts him with a touch on his shoulder. One year later, Ross calls his daughter on the phone and asks her if he and Betty know that Bruce could not have survived the explosion; Betty agrees. Ross says there are rumors that say otherwise about sightings of the Hulk and if Betty, by any chance, sees him, she would call him. Betty disagrees and tells him that she wouldn't have to due to being under surveillance watching her. After hearing her admit that she misses Bruce and loved him, Ross apologizes to her for his stubbornness towards both her and Bruce. Betty then replies, "i know you are", and ends the phone call.
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Sam Elliott accepted the role of Thunderbolt Ross without reading the script, being simply too excited to work with Ang Lee. In addition, Elliott researched Hulk comic books for the past.
Ross is sometimes thought to be the secondary antagonist of the film. This is untrue, however, as Glenn Talbot had a petty vendetta against Bruce Banner and posed as a worse threat than Ross, who in the end redeemed himself and aided Hulk into defeating David Banner, the main antagonist of the film.
Sam Elliott originally desired in reprising the role of Ross again by playing his Marvel Cinematic Universe incarnation in The Incredible Hulk. However, in spite that William Hurt was ultimately cast although Elliott would have loved to do another one, Elliott enjoyed the film and approved Hurt's casting.