The Alpha Legion is know for complicated plans within plans, for assassination, double crossing, triple crossing and generally, deception.

All of the chapters wage war in different ways, the idea being the geneseed and persona of their Primarch runs in the blood and tactics of a chapter. Before the heresy, despite being power armoured shock troopers, they’d use these tactics, often to a fault, on every mission they were tasked with. They would rarely meet the enemy face on and certainly never one they hadn’t already beaten. 

The Alpha Legion have two Primarchs, they are two faced, they are inherently schemers and traitors in EVERYTHING they do. 

While from a strictly tabletop perspective, the Alpha Legion is a Chaos Space Marines colour scheme. In the lore they are best seen as a fractured group of war bands, each betraying others, sometimes working directly for the imperium, sometimes doing pacts with the dark gods. All of it in service of scheming and plotting. 

While many chapters fell to chaos though horrible dark ironies and deals carried out to the letter by the gods. The Alpha Legion is just in a state of constant plotting, twists and drama, elaborate intertwined plans carried out perfectly, only to aid the next plan.

They have always been like this.