Before the Wars
When Revan was first being trained as a Jedi Padawan, he was found to be very strong in the Force. His close friend Malak was strong in the Force as well, though Revan was undeniably the stronger of the pair. Revan's first Jedi Master was Kreia, though he learned from several others, including Masters Zhar, Dorak, and Kae. But after learning from these Masters, he came back to learn more from Kreia. After the Jedi Civil War, Kreia was overcome with guilt and confusion about Revan's fall. She journeyed to Malachor V, where she was corrupted by the dark side, becoming Darth Traya.
Early Career
Malak and his best friend, Revan, were Jedi assigned to the Order's enclave on Dantooine. While they were there, they discovered a Star Map that had been left on the planet by the Rakata, a species that had ruled the galaxy in the distant past.
When the Mandalorian War began and Outer Rim planets began falling, Revan defied the Jedi and insisted on defending the galaxy alongside the Old Republic. The first to follow him was Malak, his closest friend. Together they rallied many young Jedi and began destroying the Mandalorians in battle after battle, finally defeating the mercenary leader, Mandalore, above Malachor V. The pair took the fleet, however, and passed beyond known space, insisting that they had to destroy the remnants of the Mandalorian armada. While beyond the Rim, they found the Star Forge, an ancient marvel of Rakatan engineering. Corrupted by the dark side energies present in and the power represented by the Star Maps and Star Forge, Revan and Malak fell to the dark side and founded a new Sith Empire out of the Jedi and Republic forces who still followed them.
Using persuasion and violence they wrested control of a large space fleet from the Old Republic and began their career of conquest. As Revan was the stronger of the two Sith Lords, he claimed the coveted title of Dark Lord of the Sith, and Malak reluctantly consented to be his apprentice. He chaffed under Revan's control, though, and awaited the opportunity to replace his master.