Abzorbaloff
You've dabbled with aliens, now meet the geniuine article.
Assuming a Human disguise and alias in the form of Victor Kennedy, the creature known as the Abzorbaloff absorbed his victims' memories and consciousness into himself.
Profile
"Abzorbaloff" is not the actual name of the species, but was coined independently by Elton Pope and the Doctor (presumably a pun on the word "absorb"), though the alien was seen to approve of the term. Other names thrown at him by the Doctor and Elton included "Abzorbatron", "Abzorbaklon", "Abzorbatrix" and "Abzorbalot".
Circa 2007, the Abzorbaloff lived the lifestyle of a wealthy Human gentleman named Victor Kennedy. When he discovered the Doctor's picture on LINDA's website (TS: Tardisode 10) the Abzorbaloff recruited them to try to locate the Doctor with the aid of Torchwood files that he had somehow obtained.
Feigning in common with the group an admiration for this mystery figure, the Abzorbaloff picked off members of LINDA one by one until he could acquire his real quarry. He planned to absorb the Doctor's memories and knowledge. He was defeated when the remnants of the absorbed members of LINDA rallied together to pull him apart from the inside. When Pope then broke the cane, the Abzorbaloff's limitation field inside it was destroyed. This caused his absorption ability to go out of control, and his body to collapse into a gooey puddle. The remnants then seeped into the ground. (DW: Love & Monsters)
Abilities
The physical absorption process was begun by a simple touch and was irreversible. The faces of his victims could be seen embedded in his flesh and retain their identity and consciousness for several days at least, but are also able to access the creature's own thoughts. As previously noted, the Abzorbaloff also required the use of a limitation field (disguised as part of Kennedy's cane or the cane itself) to keep his absorption ability in check. It would also seem that the Abzorbaloff posessed some kind of ability or technology that allowed him to change his appearance as he was able to take on the form of Victor Kennedy. (DW: Love & Monsters)
Origins
Clom, the creature's home planet, is the sister planet of Raxacoricofallapatorius. Despite a passing resemblance to them, the Abzorbaloff spoke of the Raxacoricofallapatorians with contempt. (DW: Love & Monsters) Jack Harkness implied that the Absorbaloff was a distant cousin of the Slitheen, from a family known as the "Absorbalovian Rebels". (WEB: Captain Jack's Monster Files) Also, the species name Abrobvian was given to them in the Monster Files, yet Clomian was also a candidate for species name.
Behind the Scenes
The basic design for the Abzorbaloff, and its name, came from a drawing by then 9-year-old William Grantham, an entrant to a Blue Peter competition to design a monster for Doctor Who. The on-screen Abzorbaloff remained mostly faithful to the drawing with a few changes. The drawing depicted the Abzorbaloff as about the size of a building, rather than Human-sized. As performed in the finished episode, the character resembled "Fat Bastard" from the Austin Powers film series.