Mags is the mystery Lombax who was tasked by the Lombax High Council and Ratchet's father Kaden with mapping all dimensions in existence and creating the Dimensional Map so that the lombaxes could find the perfect dimension to hide themselves in. He does not appear physically and is only heard in voice recordings that he left behind.
In Rift Apart, on planet Savali, Ratchet can find collectibles known as Lorbs; twelve in total that each contain a piece of Mags' audio diary for the optional side mission "Hunt for Lombax Lore". The Lombax Shrines that the Lorbs are contained within will only activate in the presence of a Lombax. His voice is only ever credited as "Mystery Voice" until the end of the final Lorb where his name is revealed. An automated recording of his voice is heard saying aloud "Interdimensional anomaly detected" when Ratchet approaches the Archives on Savali, causing it to enter it's defensive walking mode. After initially believing it might be impossible to map all the dimensions, he later estimated he could complete the map if given one year and three weeks with the Dimensionator, loaned to him by Kaden and very little sleep.
He was given the job after the Lombax Council liked the mapping work he had done on Savali and gave him a larger task in mapping the dimensions. As a self-proclaimed genius he felt he could do both the mapping and make enough time to keep an audio diary of his progress. Throughout his mapping diary, the dimensions that Mags describes are the worlds of various other PlayStation games and makes note that when he is done mapping, he eagerly wishes to study these dimensions more thoroughly. As the diary entries go on, Mags notices that Kaden is becoming more and more stressed, until he finally discovers the reason and that his map was to help hide their race from an upcoming threat (possibly Tachyon). In his final entry he leaves a message for any Lombaxes that were left behind and that he has left a copy of the Dimensional Map in the Archives with the location of the Lombax dimension marked down.
Redesigning the Dimensionator[]
The new converted helmet Dimensionator by Mags
After being pressured by Kaden to speed up his progress, Mags felt that the time it took to input coordinates, crank and pull the trigger on the Dimensionator was too time consuming and so to quicken the pace of mapping the dimensions, took the time to convert the design of the Dimensionator into the form of a helmet that functions on voice commands. This explains the Lombax blueprints of the Dimensionator in the Savali Archives being of a different gun-like design than the helmet-like original Dimensionator that is seen earlier in the series, starting in Tools of Destruction. When Clank repaired the broken original Dimensionator, he reconverted it back into its original form. It's unclear how Canon this lore actually is, in the Rycan V introduction video for the Dimensionator in Tools Of Destruction, it's shown the design was a hat from the start, the video taking place before the Dimensionator was used to stop the Cragmites, but according to the Lorbs found in this game, the Hat design was incorporated less than a year before the Lombax's left their own dimension to escape Tachyon.