This is such a classic and I can't believe there's no decent tab for it in this 
site, so here you go. Tempo is around 92 and you can listen to the song to get the rhythm.

Key: G

Intro with rapping:
G - G - Em - Em


Verse 1:
G                                  D/F#
I am a mountain, I am a tall tree, Oh
Em
I am a swift wing sweepin' the country 
G                                D/F#
I am a river down in the valley, Oh
Em
I am a vision and I can see clearly


Prechorus: 
C                           Am                   
  If anybody asks you who I am 
     [ch]Cmaj7/D[/ch]                                  D   
Just stand up tall, look 'em in the face and say


Chorus: 
G          D/F#               Em 
  I'm that star up in the sky 
         Em/D                  
I'm that mountain peak up high 
C        G/B
  Hey, I made it 
Am7                D4       D
  I'm the world's greatest 
G          D/F#               Em 
  I'm that little bit of hope 
        Em/D                      
When my back's up 'gainst the ropes 
C       G/B
  I can feel it
Am7                         G - G - Em - Em
  I'm the world's greatest 


Verse 2
G                            D/F#
I am a giant, I am an eagle, Oh
Em
I am a lion down in the jungle 
G                                      D/F#
I am a marching band, I am the people, Oh
Em
I am a helping hand and I am a hero


Prechorus: 
C                           Am                   
  If anybody asks you who I am 
     [ch]Cmaj7/D[/ch]                                  D   
Just stand up tall, look 'em in the face and say


Chorus: 
G          D/F#               Em 
  I'm that star up in the sky 
         Em/D                  
I'm that mountain peak up high 
C        G/B
  Hey, I made it 
Am7                D4       D
  I'm the world's greatest 
G          D/F#               Em 
  I'm that little bit of hope 
        Em/D                      
When my back's up 'gainst the ropes 
C       G/B
  I can feel it
Am7                         
  I'm the world's greatest 


Bridge:
Gm           [ch]Dm/F[/ch]          C/E
  In the ring of life I'll rain love 
Dm                 C/E      F
And the world will notice a king
Gm               [ch]Dm/F[/ch]          C/E
  Where there is darkness I'll shine a light 
Dm                 C/E            F   D7
And mirrors of success reflect in me


Chorus: 
G          D/F#               Em 
  I'm that star up in the sky 
         Em/D                  
I'm that mountain peak up high 
C        G/B
  Hey, I made it 
Am7                D4       D
  I'm the world's greatest 
G          D/F#               Em 
  I'm that little bit of hope 
        Em/D                      
When my back's up 'gainst the ropes 
C       G/B
  I can feel it
Am7                        
  I'm the world's greatest