From Halopedia, the Halo wiki
Lance O'Donnell is a famous socialite who lived in the city of New Mombasa, Kenya, on Earth. The top floor of his former residence, Ivory Tower, was used as a public park prior to the Battle of Mombasa on October 20, 2552.
His name is a reference to Martin O'Donnell, the former Audio Director at Bungie, whose sound studio is called "Ivory Towers." Lance is one of Marty's nicknames.