Jerk with a Heart of Gold: He can have control issues, but he is generally a good person determined to stop the Headmaster once he learns ie's involved in events.
Ungrateful Bastard: Lloyd comes off as a bit unfair on Dinah after the snowball incident considering that Dinah had responded to it by threatening the Headmaster. He realizes his mistake after learning that Dinah had been hypnotized by The Headmaster.
Didn't Think This Through: Occasionally, such as in "The Prime Minister's Brain" where he programmed the Super Salamada to keep out anyone with the surname "Glass" but didn't anticipate that Dinah had been renamed Dinah Hunter after the Hunters adopted her so ended up getting in anyway.
Mass Hypnosis: Attempts this at the end of the first book, and uses technology to put it into practice in the third and fifth books.
No Name Given: The Headmaster is only ever referred to by his title (although he has been referred to as 'the Director' in the fourth book), but the second and fifth books in particular make it clear that he does have a name and that SPLAT know what it is.
Would Hurt a Child: He has often shown a willingness to hurt the members of SPLAT, ranging from ordering his other 'servants' to tear them apart as old dolls to having them wrapped up and shipped away as carpets.