Nalgonas is an Aesir Titan who was present during the battles between the Titans and the Old Gods. During the time he inscribed detailed summaries of events onto runes, which became known as the Runes of Nalgonas.
According the Runes, Nalgonas used an artifact known as the Hand of the Highfather to rid the southern lands (which would be known today as Pandaria) of the corruption left by the death of Y'shaarj. Many years later, he was assigned the task of becoming a watcher for the Titan prison complex, Uldanas.
He used the Hand on numerous creations of the Titans that had been afflicted with the Curse of Flesh, and found that the creations were reverted to an earthen status. Nalgonas determined that the true purpose of the device was to cleanse the Old God corruption from anything and decided to keep it with him inside Uldanas, as he awaited the return of the Pantheon of Titans.
Yet, as he waited, he couldn't help but wonder as to why he, a Titan, was assigned to become a Watcher, rather than have a construct fill the task. Eventually, he created a Watcher construct to maintain control over Uldanas, and ventured out to rejoin his Titan brethren.
Judging by the runes, it is possible that Nalgonas was close to Aman'thul the Highfather, at least in war against the Old Gods.