Question: When I was in high school, Homer's *Iliad*, Homer's *Odyssey*, and Virgil's *Aeneid* were taught as a trilogy of sorts. 

Was Virgil the first Roman to refer to Odysseus as 'Ulysses' or was there another (recorded) author before him who did so?

Answer: 
Ulysses is the Latin form of the Greek Odysseus, stemming from the Sicilian or alternate Latin form Ulixes. The first instance of these forms in literature that I can find is in the *Odusia* by [Livius Andronicus](https://en.wikipedia.org/wiki/Livius_Andronicus#Odusia). This is an early translation of the Odyssey (third century BC). The only parts of it that survive are 46 lines from 17 books of the Odyssey, but this is one of those lines:

> 
> Inferus an superus tibi fert deus funera, Ulixes? 
>  (Od. 10, 64)
> 
> 
> 

I found the surviving text of the Odusia [here](https://en.wikipedia.org/wiki/Livius_Andronicus#Odusia). 

[Marcus Pacuvius](https://en.wikipedia.org/wiki/Pacuvius) was an early Latin dramatist who probably used Ulysses. Though I'm not sure, he wrote many of his plays on Greek topics, and the translations of his works I found use the name Ulysses. 

So to answer your question: **Livius Andronicus** was the first writer I can find who used a form of the Latin name of Odysseus, and Virgil was not the first.
I am not a linguist, but I think it's worth mentioning that the Odysseus→Ulysses transformation is a special case of something called the "Sabine L": some words that had "d" sounds in Old Latin (or in Greek) became "l" in later (classical) Latin. Examples include:

* *lacrima* in Latin from Old Latin *dacrima*, from Greek *dakry* from PIE \*dakru- from which both English *tear* and Sanskrit *aśru*.
* *olere* "smell," from the same root as *odor*
* *lingua* from *dingua* (cognate *tongue*, Sanskrit *jihvā*)
* Latin *lēvir* "husband's brother" (cf. "levirate") from \*daivēr > Sanskrit देवृ still present in Hindi as *devar*

So just to avoid any ambiguity here at this question, *Ulixes* being the Latin form of Greek *Odysseus* is not an arbitrary choice made up by some author.