He is described as being the sanest of the Fiends, being mentally stable enough to control the band of drugged psychotics and organize them into a credible fighting force, and even establishing a base of operations out of Vault 3. Ranger Bryce Anders remarks that Motor-Runner has survived several previous NCR assassination attempts, which prompted Colonel Hsu to give Anders the mission of killing the Fiend leader personally.
He is found in his throne room in the Vault 3 maintenance wing flanked by his two guard dogs, BoneGnash and GhashBone.
The Courier can sell him various drugs (Jet, Psycho, Buffout) for 20 caps (or 22 caps, if the player passes the Barter check) if you pass a Speech check at the entrance of Vault 3 when speaking to the Fiend at the door. 22 caps is more than the player will ever be able to receive from selling drugs valued at 20, with the exception of one instance involving Ricky.
If you fail a speech check when talking to Motor-Runner he will appear as hostile but will not attack.
Motor-Runner is a critical NPC for the quest Aba Daba Honeymoon, and thus it will fail immediately if he is killed. For this reason, it is best to pursue that quest first.
Additionally, if you decide to kill everyone in Vault 3 and then proceed to kill Motor-Runner for Hsu, you can still talk to him right before you kill him and give him the drugs from Jack and Diane.
If you kill him and bring back his helmet to Colonel Hsu you get an extra speech option and you will receive additional reputation with NCR.
Motor-Runner has the unique perk Motor Runner's Buff, which grants him 20% DR in addition to the 5 DT he receives from his armor and helmet. It also grants him +10 damage on all melee attacks. This unique perk is similar to the effects of the drug slasher.
If you kill Motor-Runner while the Fiends are hostile they will no longer attack unless provoked.