In George R.R. Martin's Song of Fire and Ice series one of the Kingsguard tries to kill Tyrion Lannister on the bridge of boats and drowns for his trouble. I could have sworn it was Ser Meryn Trant but I am reading A Storm of Swords now and on page 819-820 Ser Meryn is standing guard over the eight year old King Tommen. Am I mistaken?
Update:OMG I forgot about him! Thanks sooooo much for reminding me!
Verified answer
I think it was Ser Mandon Moore that attacked Tyrion on the bridge.