Bill Tanner is an antagonist in the Alex Rider book Snakehead.
When Alex Rider is captured by the Snakehead director Winston Yu he is bought to Bill Tanner's headquarters. Bill Tanner brags about Arnhem Land's dangers, saying that this region of Australia is "as bad as the world when it first began." To Alex, Bill Tanner does not look like a real doctor - first off, he wears no white coat, and he is wearing a gaudy shirt and jeans. What sets off the red flag in Alex's mind is that Bill's fingernails are dirty and his hair is unkempt. Knowing doctors are fanatical about hygiene and their appearance, Alex knows he's in something dark.
Bill Tanner is very affable, saying that he will be treating Alex good. But this makes it all the more nightmarish, because Bill shows no concern about killing a child in such a gruesome way. Bill even has the cheek to blame Alex for it, when it was really Winston Yu who provoked Alex. Bill says that he knows Alex is angry because "I'd be pretty sore too. But maybe you should have thought of the consequences when you took on the Snakehead." This is when Alex knows Bill and his staff are pure evil as he suspects strongly that they have done this ritual with many other people before.
Bill and his henchwoman, Charlene, (who it is implied he is in a relationship with) brag about the dangers of Arnhem Land and how impossible it is to escape. In his overconfidence, though, Bill does give away a crucial fact - the only two ways out are by helicopter and the water plane. Bill then goes into a lecture about how Alex has been a bad little boy so he will be donating him to charity, and Bill says that he will be splicing Alex limb by limb to give to a millionaire from Sydney.
After the customer arrives, Bill has Jacko & Quombi, his two Aboriginal henchmen, imprisons Alex in his room overnight, but Alex manages to escape. Bill is extremely angry with his henchmen for their failure and falling for Alex's tricks. Distraught at the sudden change in events, Bill goes mad and orders Alex shot down. He sees Alex escaping on the plane and rages as his hospital center burns.
Out of fear for what Yu may do to him for his failure, Tnnaere commits suicide rather than face punishment.
Bill Tanner was a cowardly, yet ambitious, man, who chose crime rather than respectability, because he was greedy, lustful and full of corruption. If Alex could see into his soul, Bill's soul would be dark, dark as a lightless cave. Bill Tanner was described as a normal looking man with blond hair, and he was darkly handsome.
He held no respect for human life, being in love with money, (and, it is implied, his secretary Charlene) and he may have been a womanizer as he liked setting himself up with young attractive female nurses. Bill was a man of order, and liked it when things were going his way - the action of a classic businessman. But when things backfired, such as when Alex fled on his plane, he went crazy. Bill and Charlene were in a warped sort of relationship, as they took sadistic pleasure in other people's suffering, and only liked bad things to happen to others, not to them - but this backfired as Bill killed himself upon failure and Charlene got arrested by MI6.