Did he take the role of his colleague or did he take over the role of his colleague?
Also take on the role sounds like a viable option to me, because i'm trying more to convey the sense of him.
Here is an example from the post getting things done when you wear multiple hats in pookiemd's blog:
I wear many hats, and i.
What is the difference between job title and job role?
For example, from the google documentation on rich snippets:
Title — the person's title (for example, financial manager).
What is the distinction between role and rôle [with a circumflex]?
What is the significance of the ô character in rôle in this work?
What is the standard rule for using or not using hyphen and.