Magmatron is a Predacon and a Dinobot in the Beast Wars and Beast Machines portions of the Generation 1 continuity
As befits a decorated Warrior-General Magmatron is capable of both elegant, reasoned judgement and wild, vicious action. Once he has set his sights on a goal his drive to achieve it is unwavering and he will accept nothing less than total victory. Despite these atributes, and prodigious physical power, Magmatron's greatest advantage often lies in his charasmatic leadership. Reveared and admired by his soldiers, Magmatron fits the title "Emperor of Destruction" better than most.
On the surface Magmatron seems to have much in common with Megatron (BW). Both are schemers and planners, willing to subvert the established Predacon power structure to suit their plans and ultimate ambition for power. Their key difference lies in their relationships to that power structure. Megatron is at heart a rebel, working outside existing society. Magmatron, on the other hand, values his position of power and eminence in the currant Predacon hierarchy, and though he schemes to someday stand at the top of that body, he is unwilling to risk his current high-standings any more than he must even to achieve those future goals.
Durring the events of Beast Machines, Magmatron found himself working as a part of a new team of Dinobots, composed at least partially of former Maximals, against the efforts of Megatron and his Vehicon hordes.
(Magmatron originated in the Japanese exclusive Beast Wars Neo line but was imported to the US during Beast Machines as one of the Dinobot subline. His Dinobot tech spec makes it clear that he is definately intended to be the same character seen in Beast Wars Neo.)
Beast Wars Neo
Manga
In the Neo manga Magmatron and all his forces were changed into Transformers from actual animals by the power of Unicron.
Anime
Beast Machines
Following the events of Beast Wars Neo Magmatron returned to Cybertron to find it overrun by Megatron's Vehicons. He joined forces with T-Wrecks and his Dinobots to combat the threat.
Transformers Universe: The Wreckers
The Dinobots, including Magmatron, are tricked and sent on an apparent suicide mission in an attempt to save Cybertron.
Beast Wars:the Gathering
Magmatron's Cybertronian form