Beginning our tour of the Solar Auxillia, the Legate Commander is a character that can be as varied as any human is. Some are tyrants. Others are benevolent commanders that are truly concerned for the well being of their troops. Some might be noble. Others rich. All of them though are experienced and have risen to the high rank of commander one way or another.
If they're upgraded to be a Lord Marshal (which you probably should for a warlord), then they gain bonuses to their personal household retinue that are well worth it. Of course, their high Ld can also be used by all other Solar Auxillia members, which will be vital in keeping them moving (and not, e.g., pinned down). With the Forged in War rule, the commander may select the warlord trait in play. This can be a useful boon, depending on the enemy and the battlefield.
Beyond this, the Legate Commander or Lord Marshal is a highly customisable character that can be taken down a number of routes in terms of builds. We'll look at some of them below.
In the world of 30k (and 40k), these warlords are going to be easy blood for enemy Space Marines. It would be wise to hold them back, or sit them in a tank to ensure that their Ld bonus is spread to the whole army for as long as possible.
There are any number of builds possible here. I'm going to just touch on a few of them to give a bit of a flavour.
Lord Marshal, artificer armour, iron halo, power fist, digital lasers, archeotech pistol (150 points)
An expensive build that is meant primarily for close combat duties. Change the iron halo for a displacer matrix if you have the points. Or maybe a cyber-familiar as well just for the improved invulnerable save.
Lord Marshal, artificer armour, melta bombs (85 points)
A cheaper build for a Lord Marshal that is meant to sit back in a tank. The melta bombs are just a deterrent really.
Legate Commander, Hand Flamer, Iron Halo (65 points)
Very cheap, vulnerable (but hopefully he's inside a tank). And that's about it. The hand flamer is just for fun.
Legate Commander, Inferno Pistol, Iron Halo, Cyber Familiar, Melta Bombs, Artificer Armour, Power Axe (115 points)
A cheapish and versatile commander.