Question: When was the character Sentinel Prime introduced in the Transformers series?

List of Primes and Matrix holders


This is a List of Primes and Matrix holders in the Transformers robot superhero franchise. "Prime" is a fictional rank in the Transformers toy and entertainment franchise created by Hasbro and Takara Tomy. The title is usually given to the leader of the Autobots and bearer of the Matrix of Leadership though there are a few exceptions, the most notable of these was in Transformers Animated, where Prime was not a title, but a commanding rank amongst the Autobots, as indicated by Optimus to Sentinel, and second only to that of Magnus. In Japanese translations of Western Transformers fiction, as well as original Japanese fiction such as Beast Wars II, the equivalent to the Prime rank is "Convoy". For example, "Rodimus Prime" would translate as "Rodimus Convoy" in Japanese, while "Lio Convoy" would translate as "Leo Prime" in English.
Transformers: Generation 1
The evidence for "Prime" being a rank in the original comic and cartoon is weaker than elsewhere, but the case can still be made. The comic would introduce the "Creation Matrix" and portray "Prime" as a religious title, while the cartoons' "Matrix of Leadership" was held by Prime as a military title. Though many Matrix-Bearers are seen, and all are by definition Autobot Leaders, only four are ever named on screen: Alpha Trion, Optimus Prime, Ultra Magnus, and Rodimus Prime. Without knowing any other names it is hard to make a concrete case here for "Prime" being a title given only to Matrix-Bearers. Two decades later, the All-Spark Almaniac, revealed the names of all the "Primes" seen in this continuity: Primon, Prima, Prime Nova, Guardian Prime, Zeta Prime, Sentinel Prime, Alpha Trion, Optimus Prime, Ultra Magnus, and Rodimus Prime.


Optimus Primal also held the matrix of leadership as well as Optimus Prime's spark for a time while Optimus Prime's body was being repaired by the Maximals.  

Beast Era
It's only passingly touched on, but may be noteworthy that the phrase, "Who died and made you Prime?" was used by Maximal characters in Beast Wars, implying that, to them, "prime" was roughly equivalent to "leader". They also used the word to mean "great" or "good" in the phrases "That's just prime," (said sarcastically), and "Feeling prime." The Beast Era would introduce a number of "Convoy" characters that would later become "Primes" when introduced into American fiction. Many of these Convoy figure were Maximal leaders who carried their own versions of the Matrix of Leadership.

Robots in Disguise

Unicron Trilogy
The Optimus Prime of the alternate universe of Transformers: Armada also possesses a Matrix (Much like the original Matrix, it serves as the symbol of the Autobot Commander). "Prime" is indeed a title given to leaders and Matrix-bearers in the Unicron Trilogy universe, as evidenced by both Vector Prime and Optimus Prime, but no other Primes are ever named. In Galaxy Force, Override (Nitro Convoy), Scourge (Flame Convoy), Evac (Live Convoy), and Metroplex (Megalo Convoy) all hold the title of Convoy as leaders of their respective planets, but this scheme does not carry over into the western translation, and so the Prime appellation does not apply. Likewise, in Super Link, the Japanese version of Energon, Rodimus is known as "Rodimus Convoy", hearkening back to the name of his G1 predecessor. But again, this does not follow through in Hasbro's materials. Vector Prime is not known as Vector Convoy in Japan, but Vector Prime, while Optimus maintains the traditional Convoy title as Galaxy Convoy.

Thirteen Original Transformers

In the fictional narrative of the Transformers universe, the Prime lineage began with the Thirteen Original Transformers created when the universe began by Primus to aid him in his battle against Unicron. They went on to become the foundation of life on Cybertron. The story concept of the Original Thirteen, as well as three of their members (Prima, Liege Maximo and The Fallen), were created by comic book writer Simon Furman.
Live-action film series

In the live action film series, the Dynasty of Primes are the first wielders of the Matrix  and used it to power a Sun Harvester. After learning that Earth contained intelligent life, they refused to use it and The Fallen fought them over it. He was too powerful for them so they stole it and sacrificed themselves to hide it. Sam Witwicky found it but it crumbled to dust in his hands. However, in a vision, the Dynasty gave it to him to wield as he proved worthy of it, telling him that the Matrix is something that must be earned not found. He used it to revive Optimus, but The Fallen took it before it completely healed Optimus. Used to power the Sun Harvester, it survived and was given back to Optimus after he destroyed the harvester.
Transformers Animated
Prime is still a rank in the Transformers Animated continuity, but (uniquely) it is distinctly lower than commander of all Autobots (that would be Ultra Magnus — the "Magnus" refers to his rank). This is revealed when Sentinel Prime attempts to give an order to Optimus Prime. Optimus is able to disregard this order because regardless of Sentinel's standing on the Cybertron Elite Guard, they are both still Primes of equal rank. The Elite Guard members, Ultra Magnus and Sentinel Prime, have bars on their forearms, with more bars present for the superior officer. Optimus Prime lacks these, and as such it is unknown if they are only present on the Elite Guard. The rank of Prime seems to be roughly equivalent to the human naval rank of captain.

Transformers:Timelines

The Convoy
In the Transformers: Timelines fiction, the Transtech formed a group known as the Convoy, made up of Primes/analogous leaders from various reality streams in order to deal with threats to the multiverse. The identities of several members of the Convoy were designated "Classified" by Axiom Nexus Security, but were made known due to the efforts of Renegades from the Go-bots universe.[7][8]

Transformers: Prime
In the "Aligned Continuity" (which includes the video games Transformers: War for Cybertron and Transformers: Fall of Cybertron, their tie-in novels Exodus, Exiles and Retribution, and the television series Transformers: Prime), the Prime rank is similar to its portrayal in the original series. "Prime" is the name given to the leader of the Autobots and holder of the Matrix of Leadership, which is passed down to a successor at the end of the current Prime's reign. Characters shown to be part of the Prime lineage in this continuity include Optimus Prime and Sentinel Zeta Prime (referred to as "Sentinel Prime" in the novels and "Zeta Prime" in the video games).

While he didn't hold the Matrix, the Autobot's human ally, Jack Darby, was entrusted with the Key to Vector Sigma, thus he was entrusted with the fate of the Matrix of Leadership and was even referred to as an "honorary Prime" at one point by Miko Nakadai. The Autobots and Megatron discovered that Unicron's spark dwelt at the center of the Earth and Prime emptied the full power of the Matrix into Unicron's spark upon travelling there. After Unicron was successfully returned to stasis, the Matrix was drained its energy, Optimus lost not merely the wisdom of the Primes, but all of his own memories since becoming a Prime.  Fortunately, it was revealed that the key allow the Matrix to be refilled, and Optimus's memory restored, via the mega-computer Vector Sigma on Cybertron. Jack and Arcee travelled to Cybertron to load the key, then returned to Earth in the midst of a battle between Orion and Megatron. Though the archivist was hesitant at first, Jack convinced him that he was in fact worthy and used the key to restore the Matrix's power and Optimus's memories.
In season three, Smokescreen was chosen by the Matrix to succeed Optimus Prime. However, Smokescreen used the Forge of Solus Prime to restore Optimus to life and therefore does not become a Prime or holder of the Matrix.
See also
Matrix of Leadership
List of Autobots
Thirteen (Transformers)