The first type, the white knight, refers to the friendly acquirer of a target firm in a hostile takeover attempt by another firm. The intention of the acquisition is to circumvent the takeover of the object of interest by a third, unfriendly entity, which is perceived to be less favorable. The knight might defeat the undesirable entity by offering a higher and more enticing bid, or strike a favorable deal with the management of the object of acquisition.
The second type refers to the acquirer of a struggling firm that may not necessarily be under threat by a hostile firm. The financial standing of the struggling firm could prevent any other entity being interested in an acquisition. The firm may already have huge debts to pay to its creditors, or worse, may already be bankrupt. In such a case, the knight, under huge risk, acquires the firm that is in crisis. After acquisition, the knight then rebuilds the firm, or integrates it into itself.