Requesting some help from someone versed in latin

Russell Crowe's character is referred to in different parts of the film as 'Maximus', 'Maximus Decimus Meridius', and 'Aelius Maximus'. 'Decimus' means 'tenth' and was a popular men's given name (praenomen). 'Aelius' is the gens name (nomen) of a well-known Roman plebeian family, which became even more famous as the name of the Emperor Hadrian, and also the Antonines, who were adopted into his family. 'Maximus' and 'Meridius' are nicknames (cognomina); these names are often bestowed on a single family member and frequently become hereditary thereafter within that particular family. They mean 'Greatest' and 'From The South', respectively.

If regular Roman naming conventions are followed in the somewhat fanciful world of Ridley Scott's 'Gladiator', Maximus' full name would be:

Decimus Aelius Maximus Meridius.

On coins it might appear thus:

DEC.AE(L).MAX.MERID.LEG.XXVII (or whatever legion number you might prefer)

Decimus is, admittedly, a peculiar choice for the Aelii, who seem to greatly prefer smaller numbers (Quintus, Sextus). Then again, maybe two Quintuses makes a Decimus; I never was any good at math.

What you have there is the correct definition of the word "alias", which is not the same.

"Aelius" is an old Roman name but was spelled "Ælius" because the Romans contracted the dipthong like Scandinavians still do today, and the "ae" is misleading and a consequence of the lack of the proper letters in English and other western languages. That is why Scandinavian alphabets have three additional letters. "Æ" for the diphtong "ae", "Ø" for the diphtong "oe" and "Å" for the diphtong "ao". They are inherited from Latin. You don`t spell them out though, but use the vowel they correspond to, somewhere in the middle of the two parts of the diphtong. The sound you use for "Aelius" is therefore the same one you use in English for the word "bat" or "camera". I know that most people, including Russell Crowe, pronounce it "Aelius" in their best English pigeon Latin. But this is of course entirely wrong. The correct pronunciation would be "Ælius" (again, just think "bat" and you`ll be fine).

Also, Roman names are gendermorph, which means that the same name has a different grammar depending on the gender. "Ælius" for a man, "Ælia" for a woman and "Ælium" for neutral. An example of the latter is Hadrian`s Wall, which was also called "Vallum Ælium", because Ælius was Hadrian`s family name. If describing a family you could also say the "Ælian" family, and then you can probably see that this is really the same name as the modern English "Alan". It even has the same sound when you pronounce it in English, namely "Æ". Most of these names never really went away. They just changed.