Even as a novice he was noticed to be talented and dedicated and his mentor, Chaplain Hasdrubael (no relations) took him under his wing and taught him the Chapter's methods. When Hasdrubael was slain during an attack on a Chaos battleship, Xavier took command and manfully completely destroyed the chaos scum.
He was regarded as the paradigm of the Chapter's values, embodying them more than any other marine in the Chapter's history. Proudly upholding the chapter's Promethean Cult, he was a powerful orator and inspiring leader and anyone from new scouts to even the Chapter Master wanted to sit in on his lectures and hear him speak.
Here is rare audio of one of his speeches, talking about how it is.
As a sign of how much of a bro the Salamanders thought he was, they gave him 'Vulkan's Sigil', said to have been used by the big man himself. It was a sign of how much regard they held for him.
He had a pretty heroic ending given to him, battling alongside his brothers against their hated foes the Dark Eldar and kept on fighting regardless of his wounds until all of the foes were dead and then allowed himself to die. Despite being dead you can still use his miniature, meaning new adventures await our mighty hero. Of course, after 3E, he's just gonna be some generic Chappy without the badass double-melee murder combo.
Heresy Era Xavier
In one of the Horus Heresy Artbook Series, there is a Salamander's Chaplain by the name Xavier. Note that this Chaplain lived ten thousand years before the actual Xavier. Coincidence? Ancestor? Previous incarnation? Who knows.