Henry Beck, usually called Harry, was the principal figure behind the modern Tube map. Today, he's commemorated by an English Heritage blue plaque at his birthplace in Wesley Road, Leyton.
Beck (1902-1974) wasn't the first to set out Underground lines diagrammatically rather than geographically, but he was certainly the most successful. The Tube map currently in use is still underpinned by the angles and rules he devised. This year marks the 80th anniversary of his map's publication in 1933, as well as the 150th anniversary of the network itself, so it's fitting Beck should receive the accolade, despite well-publicised cuts to the blue plaque scheme.
The commemoration was unveiled at 10am today by Director of London Transport Museum, Sam Mullins. Other memorials to Beck can be found at his later home in Finchley, and again at Finchley Central station.
Update: Ian Visits has photographs from the unveiling, and further notes (including some interesting trivia on the font choice).