Sentinel Prime

Sentinel Prime is the name of several fictional characters in many of the Transformers series. The first mention of Sentinel Prime was in issue #65 of the US Marvel Comics Transformers series, where he was mentioned to hold the Autobot Matrix of Leadership before Optimus Prime. 

Sentinel Prime is One of the members of the Dynasty of Primes and dedicated as the leader of the Autobots and has since appeared in a variety of forms as either Optimus Prime's mentor or friend. In the 2011 live action movie Transformers: Dark of the Moon, Sentinel was the main villain and was voiced by Leonard Nimoy. Sentinel was also the main villain of the movie Transformers One.

Print media
Marvel Comics
The 1988 British Marvel comic book The Legacy of Unicron Part 5 had a flashback to a golden Autobot dying and giving Optimus Prime the Matrix of Leadership so that Optimus could lead the Autobots.https://tfwiki.net/wiki/File:Sentinel_prime_lou.jpg Later the American comic book Transformers 65 listed every Autobot leader before Optimus and the last one was named Sentinel Prime.https://www.slashfilm.com/1669166/transformers-one-franchise-trend-sentinel-prime/

Dreamwave Comics
In 2002, a company called Dreamwave published a prequel comic called The War Within. In it, Megatron murders Sentinel Prime so the Autobots make someone named Optronix their new leader and give him the name Optimus Prime.

 IDW Comics 
In 2007, a company called IDW published a comic book called "Transformers: Megatron Origin", which was about Megatron's origin story. In it, a Senator named Decimus fires a group of miners and replaces them with machines. When one of them complains, Decimus's bodyguards kill him. Then a miner named Megatron attacks Decimus' bodyguards and accidentally kills one of them. The other miners attack the other guards but are captured and imprisoned. They then escape under Megatron's leadership. Cybertron's leader Sentinel Prime is not worried while Megatron and the others become gladiators.

When Sentinel finds out that Megatron and the others are gladiators, he sends police called The Autobots to capture them since gladiator fighting is illegal. Megatron kidnaps Decimus but Sentinel rescues him.  

Megatron and his followers then attack The Senate and kill every senator. Sentinel puts on armour and fights against Megatron but Megatron wins and kills Sentinel and steals his armour.   

Television
Appearances in Transformers: Animated
In 2007, Cartoon Network made a show called Transformers: Animated. Sentinel Prime was a character who worked for the good guys, called the Autobots, but Sentinel was arrogant, got angry a lot and didn't get along with Optimus Prime.

Movies
Live-action
In the 2011 movie Transformers: Dark of the Moon, Sentinel Prime was the leader before Optimus Prime and taught Optimus everything he knew. After Sentinel crashed into The Moon, Optimus thought he was dead and became the new leader. When Optimus finds out Sentinel is alive he wants Sentinel to be leader again but Sentinel says no. Then Sentinel betrays Optimus to Megatron and tries to teleport the planet Cybertron to Earth and enslave all humans so he can rebuild it. When Optimus tries to stop him, Sentinel tells him “the needs of the many outweigh the needs of the few.” Sentinel also kills Transformers who surrendered. When Sentinel is about to kill Optimus, Megatron realizes that Sentinel will rule the world even though Megatron wants to rule it himself. So Megatron fights Sentinel and Optimus does also. After killing Megatron, Optimus kills Sentinel.https://www.imdb.com/title/tt1399103/characters/nm0000559

Transformers One
In the 2024 movie Transformers One, Sentinel Prime is the ruler of Cybertron who turns out to be evil. When aliens called Quintessons attacked Cybertron, Sentinel betrayed the leaders of Cybertron (called the Primes) and killed them all except one Prime that he tried to kill but who survived. Then Sentinel tried to steal something called The Matrix of Leadership so he could be very powerful but it turned to dust. Sentinel lied to everyone that his name was Sentinel Prime, instead of just Sentinel. Sentinel also stole the cogs from newborn Transformers so that they couldn't transform. Sentinel made them mine the depths of Cybertron for Energon, which only The Matrix of Leadership could create, and give it to the Quintessons. And Sentinel had all the Transformers live underground so that they wouldn't know that he was doing that. When Sentinel finds out Alpha Trion is alive, Sentinel cuts his head off. Sentinel also captures most of the Transformers trying to overthrow him and he tortures one of them, named D-16, for refusing to bow to him. Sentinel also sends his second-in-command Arachnid to kill the others, only for her to be captured and forced to reveal the truth about Sentinel to everyone to start a revolution. Sentinel begs D-16 not to kill him by offering to make him his Viceroy but D-16 just wants revenge. When D-16's friend Orion Pax tries to convince D-16 not to kill Sentinel, D-16 ignores him and shoots at Sentinel but Orion puts himself between Sentinel and D-16's gun so Orion gets shot instead. Then D-16 breaks Sentinel in half, tears Sentinel limb from limb, puts Sentinel's transformation gear inside himself and renames himself Megatron. Megatron kills all of Sentinel's bodyguards and tries to make himself dictator of Cybertron. Orion Pax comes back to life as Optimus Prime and exiles Megatron for being like Sentinel.

References

Other websites
 Sentinel Prime at the Transformers Wiki
 Sentinel Prime Character Page - Transformers Animated.com

Category:Fictional robots
Category:Transformers (franchise)