Seneca Crane was the Head Gamemaker in the 74th Hunger Games, in charge of coordinating game play and ordering obstacles into the arena. At the end of the Games, he allowed both Katniss Everdeen and Peeta Mellark to emerge as victors, rather than allow them to commit suicide and thus have no victor at all. Unfortunately, this decision did not play well with President Snow, and Crane was dead by the time of Katniss and Peeta's Victory Tour six months later.
The Hunger Games (film)
Prior to the Reaping, Crane was interviewed by Caesar Flickerman about his previous experiences as Head Gamemaker, and what defined his individual style of gameplay. He was also interviewed prior to the Tribute Parade for his opinion of the "recruits" (as Caesar called them): While lacking a fully-formed opinion at that stage, Crane acknowledged that Katniss Everdeen's unexpected volunteering created an interesting turn of events, which could affect gameplay later on.
Following the tributes' individual training sessions, Crane met with President Snow to discuss Katniss Everdeen's actions and the potential problems she could cause if such actions continued: Snow questioned the basis for her receiving a training score of 11- shooting an arrow at the gamemakers (even though Katniss was actually aiming at the apple in the mouth of a roast pig); what Crane saw as a display of courage Snow interpreted as defiance, and he cautioned Crane that such actions could inspire hope - the only thing stronger than fear - and must be contained.
As Katniss' popularity continued to rise over the course of the games, so did her influence; an on-camera salute to the people of District 11 caused them to break out in rioting. Crane met with Haymitch Abernathy for advice, and to convey President Snow's need to keep Katniss (and the districts) in line: This led to the initial rule change that allowed two victors, though Snow expressed his opposition to such indulgence.
After Katniss and Peeta threatened to consume poisonous nightlock berries and leave the Games with no victor at all, Crane spared their lives and allowed both to emerge as victors, despite President Snow's opposition. In Snow's eyes, this act was the final straw and essentially marked the Head Gamemaker for death. In the book, it is never revealed exactly how Crane died, only that his death was ordered by Snow. In the film, Snow has Peacekeepers escort Crane to a room containing only a bowl of nightlock berries and lock him inside. It is likely that he committed suicide by eating some of the nightlock; In the film Catching Fire, Plutarch mentioned to Katniss that Crane decided to "quit breathing... that or it was poison berries" implying that he ate the berries and died as a result.
As a result of his actions, Seneca inadvertently paved the way for the rebellion that began in Catching Fire. Had he killed both Katniss and Peeta, the idea of rebellion would have died along with the two tributes. While his granting mercy was likely an effort to save face more than anything, it revealed an unexpected chink in the Capitol's armor; the districts now realized that despite its power, the Capitol could be made to look foolish, and its agenda undermined. Katniss being an "underdog" only lent further weight to her successful defiance. More to the point, Crane's actions ruined one of the primary purposes of the Hunger Games - they were supposed to be a reminder to the districts that the Capitol controlled their very existence, and could just as easily have had 24 people rounded up and executed at random, without giving them a chance to fight for their lives. Crane's actions would later be repeated by Plutarch, who effectively collapsed the tradition of the Hunger Games when he secretly devised a plan to rescue Katniss from the Arena.
Seneca is first mentioned by name when President Snow revealed to Katniss that Crane was executed for not killing Katniss and Peeta when he had the chance.
During her individual session with the Gamemakers, Katniss is trying to find some way to display her defiance. She ends up grabbing a dummy, hanging it from a noose, and writing the name SENECA CRANE across it with some dark red berry mixture from the camouflage station. The Gamemakers are shocked and horrified with her performance, and quickly dismiss her.
After Katniss tells Effie Trinket, Haymitch, and Peeta about her performance, Effie says, "Oh Katniss, how do you even know about that?", and she replies "Is it a secret? President Snow didn't act like it was. In fact, he seemed eager for me to know." This could mean several things; that the news of Crane's death was not widely circulated, that people didn't know President Snow was behind it, or simply that they believed whatever story had been publicized about his disappearance (the novels give no specific indication).
As the Head Gamemaker of the Hunger Games, Seneca Crane was undoubtedly a bloodthirsty, cruel individual. He openly showed pleasure in creating various dangers in the arena for the tributes, such as mutts, as well as watching the tributes kill one another. However, unlike President Snow and many of his associates, Crane was not completely corrupted and showed a degree of mercy by allowing both Katniss Everdeen and Peeta Mellark to survive the Hunger Games.
During the film, he seemed uncomfortable when interacting with President Snow, and did not fully agree with the Capitol's harsh regime. However, it was not until the double suicide threat made by Everdeen and Mellark that he finally decided to not go along with everything Snow said. This ultimately led to his execution.
In the first book, Seneca Crane is never actually seen, at least not directly. While he most likely observed the tributes' training and demonstrations, as Plutarch Heavensbee did, no physical description of him appears. This is primarily due to narrative mechanics; everything in the novels is seen from Katniss' point of view, and since Crane's name isn't mentioned until Catching Fire, it's possible that Katniss didn't even know who he was until President Snow told her. If that's the case, then she would have had no easy way of recognizing him and mentally cataloging his physical features.
In The Hunger Games film, Crane is portrayed with pale skin, light blueish-gray eyes, and dark hair. He sports a uniquely styled beard, shaved in an intricate design, and his hair appears to be heavily styled with product. The film also mentioned that the 74th Hunger Games marks Crane's third year as Head Gamemaker.
In Roman history, Seneca the Younger, also known as Lucius Annaeus Seneca, or often just Seneca; a philosopher and playwright. He was well-known in Roman society. He held a seat in the Senate, but later he was exiled. Like Seneca Crane, he was also forced to commit suicide.