Bear and I journey westwards on back of donkey (4)
I believe the answer is:
yogi
'bear' is the definition.
(cartoon character Yogi Bear)
'i journey westwards on back of donkey' is the wordplay.
'journey' becomes 'go' (I've seen this in other clues).
'westwards' says the letters should be written backwards (letters go right to left or from 'east' to 'west').
'on' means one lot of letters go next to another.
'back of' indicates one should take the final letters.
The last letter of 'donkey' is 'y'.
'i'+'go'='igo'
'igo' back-to-front is 'ogi'.
'ogi' put after 'y' is 'YOGI'.
'and' acts as a link.
(Other definitions for yogi that I've seen before include "Follower of a Hindu philosophy involving mind and body" , "Hindu mystic" , "Cartoon bear; Hindu ascetic" , "Master of a Hindu philosophical system" , "Practitioner of yoga" .)