The Master

In a universe other than that which the Doctor called home, a particularly incompetent version of the Master attempted to destroy the Ninth Doctor on the planet Tersurus.

While spying on the Doctor, the Master inadvertently enabled two way communication and unwittingly revealed his plans to eliminate the Doctor. After the two had arranged to meet on Tersurus, it became apparent the Master had travelled back in time to bribe a Tersuron architect to install traps in the castle they were now in. Unbeknownst to him, the Doctor had also done the same, bribing the architect with food to change the traps' details. This led to the Master floundering around the sewers of Tersurus for centuries, after which he was forced to ally himself with the Daleks and then used his very own TARDIS to travel back to the point just after he fell. Then he threatened the doctor once again with the daleks, as the Daleks were the only life-forms without noses and hence the only creatures willing to work with him.

As part of this alliance, the Master had himself "augmented" with Dalek technology, resulting in a more youthful appearance and "Dalek bumps" on his chest. Although he remained adamant they were etheric beam locators, the Doctor continually teased the Master because they resembled breasts.

When he believed the Twelfth Doctor to have been killed by the zectronic beam, the Master renounced his evil ways before the Doctor regenerated into a female form. Attracted to each other, the Time Lords walked off, arm in arm.

_{Biography from the TARDIS Data Core article, licensed under CC-BY-SA}